3rd Quarter 2002-Vol. 8 No. 3
Recent climate anomalies
in Micronesia and in the central Pacific indicate that El Niño is
occurring. The future strength and duration of the current El Niño
event is not yet known, and a suite of international computer forecasts
are split roughly 50-50 on the further intensification of El Niño
in 2002. The following ENSO diagnostic discussion was posted on the
U.S. Climate Prediction Center web site on August 8, 2002*; it states,
(*Please see the appendices for the September 19, 2002 ENSO Advisory)
“Warm episode (El Niño) conditions prevailed during July, as SST anomalies (departures from average) remained greater than +1°C throughout the central equatorial Pacific between 170°E and 120°W. Atmospheric indicators of a warm episode (El Niño) include consistently negative values of the Southern Oscillation Index (SOI), since May 2002, and weaker-than-average low-level easterly winds during May-July 2002 throughout the Pacific.
The rainfall during the first half of 2002 has been near normal to wetter than normal throughout Micronesia and in American Samoa (Figure 1). Many of the island groups of Micronesia have recently experienced some extreme rain events related to tropical cyclones. Eight tropical cyclones have passed through the region during January-July 2002 causing substantial short-term rain events. For example, of the approximately 16 inches of rain during February at WSO Chuuk, nearly 7 inches of it fell on February 28 as Tropical Storm Mitag passed near this station. A disaster occurred at Chuuk on July 02 when Tropical Storm Chataan nearly passed over the island. Rainfall amounts of almost 20 inches in 24 hours resulted in landslides that killed 47 people. Chataan also affected Guam with up to 20 inches of rain in 24 hours, and flood-levels of rivers in the south of that island were at historical highs. One-hour and 3-hour rainfall totals of 6.5 and 12.2 inches respectively surpassed 100-year return values. Fortunately, no lives were lost on Guam when the winds and extreme rains of Chataan struck on the 5th of July.
Persistent dry conditions occurred only in the Northern Mariana Islands north of Rota such as at Tinian and Saipan, and in the northernmost of the Marshall Islands (Figure 1). The persistent drier than normal conditions at Pingelap are hard to explain, given the wet conditions at most places in the Caroline Islands. Perhaps this reflects a natural distribution of rain in a convective environment that includes passing tropical cyclones. American Samoa has now entered a period of persistent wetter than normal weather.
On the large scale, the monsoon trough has remained active in Micronesia for the first half of 2002 with westerly winds extending well eastward into the eastern Caroline Islands and often as far east as the southern Marshall Islands. During January to July 2002, eight numbered tropical cyclones passed through parts of Micronesia: Tropical Storm Tapah (01W), Super Typhoon Mitag (02W), Tropical Depression 03W, Tropical Depression 04W, Typhoon Hagibis (05W), Super Typhoon Chataan (08W), Typhoon Halong (10W), and Super Typhoon Fengshen (12W). Also, for the first time since the 1997 El Niño, a tropical cyclone named by the Central Pacific Hurricane Center (CPHC) in August 2002 -- Ele (02C) -- became a hurricane.
Unusually persistent episodes of westerly winds at low latitude in Micronesia (continuing from the spring into the summer) and tropical cyclones (in the spring) are typical signs of El Niño . The following climate anomalies are typical of an El Niño year:
(1) A warming of the SST in the central and eastern equatorial
(2) A fall of the SOI to persistently negative values near –0.5 or lower (especially from April onward);
(3) The formation of “early season” tropical cyclones in the Caroline Islands from March through June;
(4) An eastward expansion of the formation region of tropical cyclones into the eastern Caroline Islands and the Marshall Islands — in extreme El Niño years like
1997 the formation region of tropical cyclones can be pushed eastward to the south of Hawaii late in the year (ie: Super Typhoon Paka);
(5) A fall in the sea level heights, beginning in western Micronesia and propagating eastward and southward.
Sea surface temperatures (SSTs) across the tropical Pacific are generally warmer than normal, with a distribution of a band of greater than +1°C persisting along the equator from about 175°E to 135°W. Weak cool anomalies are still found adjacent to South America. SST remains near normal throughout Micronesia.
The temperature of the sub-surface ocean water
has recently shown a substantial warming in the central Pacific and is
generally at least 1ºC warmer than normal to a depth of over 200 meters
in the equatorial Pacific from 160°E eastward to the longitude of Hawaii
(~150°W). Warm sub-surface temperatures of over 3°C warmer-than-normal
are found along the equator between these same longitudinal bounds.
Peak warm anomalies at depth occur near 165°W, where the temperature
at 150 meters is over 4ºC warmer than normal. Near the South American
coast, sub-surface ocean temperatures are generally near normal.
Warm sub-surface temperature anomalies that are greatest east of the date
line are typical of El Niño.
The Southern Oscillation
Index (SOI) has now averaged near -1.0 since May. During January
through July 2002, the SOI values were: January (+0.4), February
(+0.9), March (-0.9), April (-0.4), May (-1.2), June (-0.7), and July (-0.7).
Nearly all El Niño events are associated with a persistently negative
SOI. A persistently negative SOI is expected for the remainder of
TROPICAL CYCLONE ACTIVITY
Western North Pacific tropical cyclone activity from April through June, 2002 included 9 tropical cyclones: Tropical Depression 04W, Typhoon Hagibis, Tropical Depression 06W, Typhoon Noguri, Super Typhoon Chataan, and Typhoon Rammasun. During July, there were an additional 6 tropical cyclones in the western North Pacific basin: Typhoon Halong, Typhoon Nakri, Super Typhoon Fengshen, Tropical Storm 13W, Typhoon Fung-wong, and Tropical Storm Kalmaegi. Note: Chataan and Ramassun formed at the end of June and spent the majority of their lives in July. Several of these tropical cyclones formed in Micronesia and passed through many of the island groups. Super Typhoon Chataan was a costly and deadly typhoon for Micronesia. Passing first through Chuuk State as a tropical storm, its heavy rains of nearly 20 inches in 24 hours caused landslides that killed 47 people in Chuuk. Chataan passed directly over Guam on the 5th of July and caused extensive damage to homes, businesses, vegetation, and the electrical and water systems.
Based on El Niño in 2002 (and other climatic factors), a near normal to a slightly above normal number of tropical cyclones in the North Pacific is anticipated for 2002.
Two groups have issued forecasts for western North Pacific typhoon activity in 2002: The Laboratory for Atmospheric Research (LAR) at the City University of Hong Kong (http://aposf02.cityu.edu.hk/~mcg/index.htm), and The Benfield Greig Hazard Research Centre, University College London (UCL), UK (http://tropicalstormrisk.com). The Hong Kong group forecasts 27 tropical cyclones of at least tropical storm intensity (versus a normal of 28), and 17 typhoons (versus a normal of 18). The UCL group forecasts 31 tropical cyclones of at least tropical storm intensity and 21 typhoons. The University College London (UCL) forecast of enhanced typhoon activity in the western North Pacific for 2002 is based on the anticipation that the SST in the Niño 4 region of the Pacific (5°N-5°S ; 160°E-150°W) will be about 0.5°C warmer than normal during the summer months.
Another factor to consider
is that during El Niño (even a weak event), the formation region
of tropical cyclones shifts eastward into the eastern Caroline Islands
and the RMI. The risk of tropical cyclones for Guam, the CNMI, the
eastern Caroline Islands, and the RMI is increased during an El Niño
year. Also, during an El Niño year, tropical cyclone activity
gets off to an early start with an increased number of tropical cyclones
in the “early season” period of March through mid-July. (This has
already occurred with eight tropical cyclones affecting Micronesia through
mid-July.) For the remainder of 2002, several tropical depressions
may form in Pohnpei and Kosrae States and in the RMI. One or two
of these could become tropical storms in eastern Micronesia, and intensify
to typhoons as they move northwestward out of the FSM to threaten Guam
and the CNMI as full-fledged typhoons.
LOCAL VARIABILITY SUMMARIES
State of Hawaii: Mainly moderate trade winds occurred over the Hawaiian Islands during the month of August. Several upper level troughs near the island chain helped induce localized heavy showers that produced some minor flooding problems.
The most significant event occurred on 12 August when heavy showers over portions of east Kauai caused a rapid rise in water levels within Wailua River. Several kayakers required rescue from the waterway and Civil Defense officials reported one injury.
Heavy rainfall and minor flooding also occurred on 26 August in Kona, 29 August over leeward Kohala, and 30 August in Kau. These rainfall events did not cause any flood-related damages or injuries.
The passage of Tropical Storm Alika and Hurricane Ele to the south and the remnants of Hurricane Fausto to the north of the Hawaiian Islands did not have a direct impact on the island chain’s rainfall.
Kevin Kodama-Senior Service Hydrologist, NWSFO Honolulu, Hawaii
American Samoa: Rainfall at Pago Pago Airport for April, May, and June was 17.84 inches (148%), 11.20 inches (113%), and 5.92 inches (80%), respectively, amounting to 119% of normal for the 3-month period. After many months of mostly below normal rainfall during 2001, it has been wetter than normal in American Samoa for most months so far during 2002; including: March, April, May, and July. Heavier than normal rain events during the first half of 2002 have accompanied periods of an active South Pacific Convergence Zone.
Rainfall in American Samoa is not as closely tied to ENSO as it is in other regions of the Pacific. However, some prolonged very dry periods at American Samoa have occurred in association with major El Niño events, and some prolonged very wet periods have occurred in years prior to major El Niño events. Still, on average there is not a consistent ENSO signal in the rainfall. There is a tendency for Samoa to experience prolonged dry periods in the years following intense El Niño events, such as 1997-98, and to be wet during weak to moderate El Niño years. With 2002 now looking to be a weak to moderate El Niño, the recent surplus of rain is typical. If a very intense El Niño develops during 2002 (which is not likely), then a prolonged dry period may commence in early 2003.
With the onset of El Niño in 2002, the risk of a damaging tropical cyclone may increase for Samoa during its December 2002-March 2003 cyclone season.
Predicted rainfall for American Samoa from August 2002 through July
Guam/CNMI: Rainfall at Guam International Airport (GIA) during April, May, and June was 1.34 inches (34%), 6.32 inches (104%), and 7.16 inches (111%), respectively. This amounted to 90% of the normal value for the period January-March. Andersen Air Force Base (AAFB) measured 1.85 inches (38%), 8.75 inches (133%), and 5.11 inches (81%), or 88% of the average rainfall for April-June. For the first six months of 2002 (January to June) GIA received a total of 31.88 inches of rain and AAFB received 39.55 inches of rain. This was 111% and 121% of normal, respectively. In April 2002, almost daily grassland wildfires (typical of Guam’s dry season) commenced; however, timely rains in May from the near passage of Tropical Storm Hagibis and other tropical disturbances put a quick end to the wildfire season. During July, two typhoons – Chataan and Halong –affected Guam. The first, Typhoon Chataan, passed directly over the island on July 05 bringing destructive high winds and very heavy rainfall. Guam was declared a disaster area by President Bush following the devastation wrought by this typhoon. The second typhoon (Halong) passed 90 n mi to the south of Guam on July 10 with lesser winds and lighter rain amounts on island than those that occurred with Chataan. Little additional damage occurred, but the second typhoon interrupted progress in the recovery from Chataan. July 2002 was the wettest July on record for Guam with island-wide totals of approximately 30 inches. (Roughly a third of this was from the typhoons and the rest from extensive monsoonal rains during the remainder of the month.) At GIA the July total of 29.80 inches far exceeded the normal 10.53 and also far exceeded the previous wettest July total of 18.03 inches recorded in1962. A direct strike on Guam by a typhoon during July is actually a rare event. The only other typhoon to pass directly over Guam during the past 100 years occurred on July 06, 1918.
On Saipan, it was not nearly as wet during the first half of 2002 as it was on Guam (both in absolute amount and percentage of normal). Typically there is a strong decrease of rainfall amounts with increasing latitude during the dry season (January to June). Therefore, some heavy rain events on Guam, caused by tropical cyclones and other tropical disturbances passing to the south, did not reach Saipan’s latitude. Rainfall at the Saipan International Airport (SIA) for April, May, and June was 3.73 inches (133%), 2.33 inches (53%), and 1.41 inches (30%), or only 63% of the average for the period. For the same months, Capitol Hill’s measured rainfall was much higher than at the airport with 4.36 inches (125%) in April, 5.28 inches (96%) in May, and 2.08 inches (36%) in June. The 12.80 inches of rainfall at SIA for the first six months of 2002 was only 66% of normal. At Capitol Hill, 23.80 inches of rain fell during the first six months of 2002, and this was near normal at 98%. Capitol Hill’s 23.80 inches of rain during the first half of 2002 was the highest recorded rainfall during the quarter among all Saipan stations.
Rainfall amounts for April, May, and June at the Tinian Airport were 4.67 inches (133%), 4.83 inches (88%), and 1.87 inches (32%), respectively. The 3-month rainfall for Tinian Airport was below normal at 77%. At Rota Airport, April, May, and June rain amounts were somewhat higher than at islands to the north. The April, May, and June totals were 4.27 inches (94%), 6.22 inches (98%), and 4.12 inches (66%), respectively. This gave a 3-month average of 86%. On the northern part of Rota, at the beautiful Rota Resort and Country Club, the NASA TRMM network recorded a total of 26.54 inches of rainfall during the first half of 2002 versus 33.43 at the airport, or 79% of the airport total.
Based on 30 years of rainfall data, El Niño years on Guam and the CNMI average slightly wetter than normal. This should be expected since monsoon and tropical cyclone activity are normally greater during these years. Guam’s wettest year on record (1976) was an El Niño year. The extreme rainfall of that year was, in large measure, a result of the near passage of many tropical disturbances and tropical cyclones, and a direct hit by Typhoon Pamela in May. A recent El Niño year, 1997, was also very wet, in large measure due to the rains from Super Typhoon Paka, and an extremely wet southwest monsoon during most of August.
The very dry conditions that follow an El Niño year tend to start in November and carry 4-7 months into the following year. A weak El Niño event began in the first half of 2002, however it is still too early to predict whether it will increase in strength to a moderate or strong event. An El Niño event (of any strength) in 2002 would likely produce greater than average rainfall overall in Guam and the CNMI through October 2002, with persistent dryness beginning thereafter. An early start of tropical cyclone activity has already been noted in the western North Pacific basin. The typhoon threat for Guam and the CNMI should remain slightly elevated for the remainder of the year, with September through November being the months of greatest threats. Most of these will approach from the east-southeast.
Predicted rainfall for the Mariana Islands from August 2002 through
September 2003 is as follows:
Yap State: During the first half of 2002, most months were drier than normal at the Yap Airport. Only February with 6.73 inches (113%) and June with 24.10 inches (189%) were wetter than normal. The very high rain total during June at the Yap Airport was partly the result of heavy monsoonal rains that occurred when Typhoon Rammasun developed west of the island in late June. For the second quarter of 2002, the weather station at the Yap Airport recorded 5.42 inches (94%) in April, 4.30 inches (47%) in May, and 24.10 inches (189%) in June, or 123% of normal rainfall for the three months. The total rainfall for the first half of 2002 of 51.24 inches was 107% of normal. April, May, and June rainfall amounts on Ulithi were 5.85 inches (119%), 9.69 inches (126%), and 13.54 inches (125%) or 124% for the 3-month period. For the 6-month period January through June 2002, the 41.37 inches of rain at Ulithi was 104% of normal. Farther south at Woleai Atoll (which is normally wetter than Yap year-round), the rainfall was 9.63 inches (88%) in April, 16.50 inches (135%) in May, and 20.67 inches (159%) in June, for a 3-month average of 129%. The total rainfall for the first half of 2002 of 65.22 inches was 104% of normal.
El Niño years at Yap average slightly wetter than normal. This should be expected since monsoon and tropical cyclone activity are normally greater during these years. The very dry conditions that follow an El Niño year tend to start in November and carry into the year following El Niño. An El Niño event has begun in 2002, however it is still to early to predict whether it will be weak, moderate or strong. Regardless of the eventual strength of the 2002 El Niño, Yap State should experience slightly greater than average rainfall overall during this forecast period, with persistent dryness beginning late in the year. Tropical cyclone activity has already had an early start in Yap State with the passage of Mitag in early March, and a brush by the developing Rammasun in late June. The tropical cyclone threat should be normal in Yap State for the second half of 2002.
Predicted rainfall for Yap State from August 2002 through September
2003 is as follows:
||Yap Outer Atolls:|
||Island S. of 8N N. of 8N|
||90% 85% 90%|
||60% 70% 60%|
||90% 85% 90%|
Chuuk State: During April, May, and June, the weather station at Weno Island measured 18.74 inches (152%), 12.53 inches (102%), and 20.54 inches (175%). This amounted to 142% of normal amounts for the 3-month period. The very wet conditions during April through June 2002 were largely the result of a persistent monsoon trough stretching through the Caroline Islands. A persistent monsoon trough in the Caroline Islands from spring into the summer months is typical for an El Niño year. The total of 63.88 inches of rain at the Chuuk weather station at Weno for the first six months of 2002 was 104% of normal. In the Mortlocks at Lukunoch, rainfall for April, May, and June, was 12.80 inches (104%), 10.86 inches (89%), and 22.63 inches (193%) for the respective months. The 3-month average was 127%. Most of the islands of Chuuk State were wetter than normal from April through June.
Chuuk State was devastated July 02 when then-Tropical Storm Chataan’s heavy rainfall triggered 30 landslides, killed 47 people, injured dozens and left more than 1000 homeless. The following are excepts from a preliminary assessment of the landfall of typhoon Chataan on Chuuk, Guam, and Rota by Chip Guard (National Weather Service Forecast Office, Guam), Mark Lander (Meteorologist, University of Guam), and Bill Ward (National Weather Service Forecast Office, Guam):
“ … On 01 and 02 July, the rain field associated with Chataan was very asymmetric, with an area of extremely heavy rainfall and deep convection on the west side of the circulation. This area of convection moved slowly over the Lagoon on 02 and 03 July, dropping nearly 20 inches of rain
… surface wind and pressure observations from the Weather Service Office (WSO) at Chuuk, suggest that the circulation center [passed] just south of Weno Island. … Peak winds observed at WSO Chuuk were from 240 degrees [southwest] at 29 knots (33 mph) with gusts to 44 knots (51 mph) at 0550 UTC on 03 July.
… Rainfall at Chuuk was extremely heavy, especially in the 24-hour period prior to the tropical storm passage. A large persistent mesoscale convective area on the west side of Chataan produced very heavy rain, which persisted for a long period over the lagoon due to its large size and the slow movement of the system. From 01 July 1200 UTC until 02 July 1200 UTC … 19.92 inches of rain were recorded at the weather station at Weno Island, Chuuk. In the 12 hours from 01 July 1800 UTC to 02 July 0600 UTC, the weather station recorded 14.21 inches.
… Due to the very heavy rainfall on 01 and 02 July and the saturated soil, there was extensive flooding of low-lying areas and at least 30 devastating mudslides. These mudslides on several Chuuk Lagoon high islands killed 47 people, creating the greatest natural loss of life on Chuuk in recorded history.”
Rainfall for all of Chuuk State is expected to be wetter than normal at least until October as the monsoon trough and its associated tropical disturbances affect the Caroline Islands. High month-to-month variability is possible whenever rainfall is produced by an active monsoon trough and its associated tropical disturbances, and short spells of hot dry weather can be expected through September. Tropical cyclone activity began early in the Caroline Islands with both Mitag in late February and Tropical Depression 04W in April passing through Chuuk State. Tropical cyclones have continued to affect Chuuk State through July. The tropical cyclone threat should be normal in Chuuk State for the second half of 2002. Most of the tropical cyclones forming near Chuuk will be in their early weaker tropical depression stages and will later move northwest to become tropical storms and typhoons. (Although, as has been seen many times before, the weak stages of tropical cyclones may still unleash extremely heavy rainfall that can cause life-threatening flooding and mudslides.) Chuuk will have a chance of getting another tropical storm in the months of October and November.
Predictions for Chuuk State from August 2002 through September 2003
are as follows:
||Chuuk Outer Atolls:|
||Lagoon Southern/Western Northern|
||105% 105% 100%|
||95% 95% 95%|
||70% 70% 70%|
||90% 90% 90%|
Pohnpei State: Rainfall at Pohnpei State during April through June was wetter than normal at most islands. Only Pingelap registered a drier than normal total of 71%. The highest measured rainfall total at any station in Pohnpei State during April to June 2002 was the 65.02 inches (123%) recorded at the weather station at Koror. The greatest departure from normal at any station in Pohnpei State during April through June was at Kapingamarangi, where the 3-month total of 44.05 inches was 196% of normal. The monsoon trough was persistent across the Caroline Islands during April through June with several episodes of southwesterly wind and heavy rain showers. Several tropical disturbances and the beginning stages of named tropical cyclones affected Pohnpei State. At the weather station at Kolonia, the April, May, and June rainfall totals were 22.11 inches (134%), 21.35 inches (112%), and 21.56 inches (126%), respectively. This amounted to a 3-month value of 123% of average precipitation. The total of 100.62 inches of rain at the weather station at Kolonia for the first 6 months of 2002 was 112% of normal. At Pingelap, observed rainfall in April, May, and June was 14.34 inches (84%), 8.01 inches (47%), and 14.45 inches (89%), respectively, for a 3-month amount of 71%. At Nukuoro, April through June precipitation amounts were 19.53 inches (130%), 13.53 inches (92%), and 22.44 inches (184%), respectively, for a 3-month amount of 132%. Kapingamarangi picked up a substantial amount of rain during April through June as convection associated with persistent equatorial westerly wind flow produced abundant rains. April, May, and June rainfall measurements there were 18.78 inches (138%), 10.27 inches (99%), and 15.00 inches (207%) respectively. The 6-month average for the first half of 2002 was 127% of normal. Convection along the equator and enhanced monsoonal westerlies have kept Kapingamarangi in rainfall surpluses for almost every month since April 2001.
Rainfall for all of Pohnpei State is expected to be wetter than normal through at least October as the monsoon trough and its associated tropical disturbances affect the Caroline Islands. High month-to-month variability is possible whenever rainfall is produced by an active monsoon. Thus, some periods of hot dry weather are likely to occur. Tropical cyclone activity had an early start in Pohnpei State with the formation in late February of Typhoon Mitag, and Tropical Depression 04W in early April. The tropical cyclone threat should be normal in Pohnpei State for the second half of 2002. Most of the tropical cyclones near Pohnpei will be the precursor tropical disturbances that will form or move over Pohnpei, and later move northwest and become tropical storms or typhoons. Pohnpei will have a chance of getting a tropical storm, primarily during the months of October through December.
El Niño years at Pohnpei average slightly wetter than normal. This should be expected since monsoon and tropical cyclone activity are normally greater during these years. The very dry conditions that follow an El Niño year tend to start in November and carry into the year following El Niño. It is still too early to predict whether the weak 2002 El Niño event will become moderate or strong; but an El Niño event of any intensity in 2002 would likely produce slightly greater than average rainfall overall in Pohnpei during this forecast period, with persistent dryness beginning late in the year.
Predicted rainfall for Pohnpei State from August 2002 through September
2003 is as follows:
||Pohnpei Outer Atolls:|
||Island Eastern Southern Equatorial|
||105% 105% 110% 110%|
||95% 100% 95% 95%|
||75% 75% 75% 70%|
||90% 90% 85% 80%|
Kosrae State: Rainfall at Kosrae (SAWRS) during April, May, and June was 22.41 inches (103%), 15.17 (81%), and 14.51 inches (76%) respectively. The 3-month total of 52.09 inches was 87% of the normal total of 49.41 inches. Dominated by substantially wetter than normal rains during January and March, the total of 114.87 inches during the first half of 2002 was 106% of normal. The abundant rainfall in the first quarter of 2002 occurred in association with the tropical disturbances that became Tropical Storm Tapah and Super Typhoon Mitag. To illustrate the variation of rainfall among Kosrae stations, the 6-month measured rainfall for the first half of 2002 was 114.87 inches at SAWRS, 112.88 inches at Tofol, and 95.67 inches at Utwa. The variation of rainfall from place to place on Pacific high islands is a topic of much interest. On the Hawaiian Islands, the rainfall is greatly affected by the terrain, and average annual rainfall can vary over 100 inches between stations only a few miles apart. On Guam the mean annual rainfall varies about 20 inches from the wettest location to the driest location. It is not yet known to what extent some areas are wetter than others on Kosrae.
Rainfall for Kosrae is expected to be above normal from May through October, followed by below normal rainfall for the remainder of the forecast period. However, high variability should be expected in the month-to-month rainfall amounts. In keeping with El Niño onset in 2002, some tropical disturbances that later became tropical cyclones have already formed near Kosrae: the tropical disturbance that became Tropical Storm Tapah in January, the tropical disturbance that became Super Typhoon Mitag in late February, and the tropical disturbance that became Tropical Depression 04W in early April. There is a slight risk that Kosrae could experience one or two periods of rough seas, gusty winds, and heavy rains from developing tropical cyclones forming north of Kosrae State during October through December 2002. Dry conditions associated with El Niño may begin in late 2002.
Predicted rainfall for Kosrae State from August 2002 through September
2003 is as follows:
Republic of Palau: Rainfall at Koror during April, May, and June was 6.04 inches (70%), 14.13 inches (118%), and 27.39 inches (159%), respectively. The 3-month average was 125% of normal. For the three months of April, May and June, the monthly rainfall distribution at Nekken Forestry was a bit drier than at the airport (only because it did not get as much rain during June) with 9.49 inches, 14.92 inches, and 17.27 inches respectively. Farther south at Peleliu, rainfall totals for April, May and June were 7.87 inches, 12.74 inches, and 19.01 inches respectively. During the first half of 2002, the total rainfall at Nekken Forestry was 63.29 inches (96% of normal), and at Peleliu it was 61.05 inches (93% of normal) – each a bit drier than at Koror where the total for the first half of 2002 was 74.23 inches (113%). The very heavy rainfall during June in Palau was largely a result of persistent monsoonal rains and heavy rain associated with the developing Typhoon Rammasun that formed very close to the island late in the month.
The weak El Niño now in progress may strengthen during the remainder of 2002, however, it is still too early to predict whether it will do so. El Niño years at Palau average wetter than normal through September, then dry conditions set in for an extended period. The very dry conditions that follow an El Niño year tend to start in October and carry into the year following El Niño. In keeping with El Niño onset in 2002, some tropical cyclones have already formed in Micronesia and passed near Palau: Tropical Storm Tapah in January, Super Typhoon Mitag in early March (that caused some minor property damage in some parts of Palau), Tropical Depression 03W in mid-March, and Typhoon Rammasun in late June. With higher tropical cyclone activity expected eastward near the date line in the late season, the tropical cyclone threat for Palau will likely be near normal until September, and then less than normal from September through December.
Predicted rainfall for Palau from August 2002 through September 2003
||Koror and Outer Atolls:|
||Mountain Is N. of 8N S. of 8N|
||105% 100% 100%|
||95% 90% 90%|
||70% 60% 70%|
||90% 85% 85%|
Republic of the Marshall Islands (RMI): Abundant rainfall in the second quarter of 2002 occurred in association with several tropical disturbances and other mesoscale convective features at the eastern end of the monsoon trough. The Majuro weather station (representative of the southern islands) measured 8.43 inches (82%), 14.40 inches (129%), and 15.77 inches (136%) during April, May and June respectively. For the 3-month period, the average for Majuro was 117% of normal. Rainfall at Kwajalein (and nearby Ebeye) was 7.72 inches (102%) in April, 11.97 inches (120%) in May, and 11.61 inches (121%) in June, for a three month average of 115%. Kwajalein (representative of the central islands) was dry for 10 of 12 months in 2001 (only October and November were wetter than normal). Now in 2002 Kwajalein has been wetter than normal every month since January. During July 2002, Kwajalein received 22.29 inches (more than double the normal 10.44). This was a record rainfall for the month of July and the sixth wettest monthly rainfall for any month. Farther north, Wotje continued to be the driest of the locations in the RMI that measured rainfall, with 3.29 inches in April, 6.80 inches in May, and 4.22 inches in June. The rainfall totals for the first 6 months of 2002 at Majuro, Kwajalein, and at Wotje were 61.97 inches (111%), 41.35 inches (106%), and 20.39 inches (55%) respectively.
The weak El Niño event now in progress may strengthen during the remainder of 2002, however, it is still too early to predict whether it will remain weak, or become moderate or strong. Rainfall during El Niño years in the RMI averages near normal, and then dry conditions set in for an extended period in the first 4-6 months of the year following strong El Niño events. After weak El Niño events, the rainfall at Kwajalein and the northern islands of the RMI tends to be below normal, but remains near normal at Majuro. So far in 2002, there has been an early start of tropical cyclone activity in the western North Pacific, with development of tropical disturbances in the RMI, some that later moved west and became tropical cyclones. The tropical cyclone threat for the RMI should be above average for the remainder of the year, with October through December being the months of greatest threats when the monsoon trough should extend eastward into the RMI.
Predicted rainfall for the RMI from August 2002 through September 2003
||Southern Central Northern|
||Islands Islands Islands|
||105% 105% 100%|
||100% 100% 90%|
||90% 95% 75%|
||95% 95% 90%|
Long-Lead Outlook for Hawaiian Islands issue dated 19 September 2002, from NOAA's Climate Prediction Center (CPC).
ENSO ADVISORY: issued by Climate Prediction Center/NCEP on September 12, 2002
Warm episode (El Niño) conditions prevailed during August, as SST anomalies (departures from average) remained greater than +1°C throughout the central equatorial Pacific between 175°E and 130°W, and positive subsurface temperature departures and a deeper-than-average oceanic thermocline prevailed throughout most of the equatorial Pacific. Atmospheric indicators of a warm episode (El Niño) include consistently negative values of the Southern Oscillation Index (SOI) since March 2002, and weaker-than-average low-level easterly winds since May 2002 throughout the equatorial Pacific. In addition, during August above-average precipitation was observed over the tropical Pacific, especially in the vicinity of the date line (180°W), while drier-than-average conditions prevailed over many sections of Indonesia, Mexico and Central America. These oceanic and atmospheric conditions reflect the presence of El Niño conditions.
The Madden-Julian Oscillation (MJO) has been a major source of week-to-week and month-to-month variability in the atmospheric circulation of the tropics and subtropics. The MJO contributed to substantial weakening of the low-level easterly winds throughout the equatorial Pacific during late May and again in early July. During August the MJO weakened, as a more persistent pattern of weaker-than-average easterly winds and enhanced cloudiness and precipitation developed over the central equatorial Pacific. Most coupled model and statistical model forecasts indicate that El Niño conditions are likely to continue through the end of 2002 and into early 2003. Although there is some uncertainty in the forecasts about the timing and intensity of the peak of this warm episode, all of the forecasts indicate that it will be weaker than the 1997-98 El Niño. It is important to add that the global impacts of this warm episode should generally be weaker than those observed during the very strong 1997-98 El Niño. However, strong impacts are still possible in a few locations.
Based on the current conditions in the tropical Pacific, on the SST predictions, and on results from historical studies of the effects of ENSO, we expect drier-than-average conditions to continue over Indonesia and eastern Australia during the next several months, and wetter-than-average conditions over southeastern South America during the next three months. Over North America drier-than-average conditions are expected in the Pacific Northwest and mid-Atlantic states during fall 2002 and in the Ohio Valley states during winter 2002-2003. Wetter-than-average conditions are expected in the Gulf Coast states during winter 2002-2003, and warmer-than-average conditions are expected in the northern tier of the conterminous United States, southern/southeastern Alaska, and western and central Canada during late fall 2002 and winter 2002-2003.
SPECIAL SECTION-Markov Model for Pacific SST and sea level
These are the latest results of a CPC model being produced by Dr. Yan Xue. Forecasts of the tropical Pacific SST and sea level anomalies are presented here using a linear statistical model (Markov model). The Markov model is constructed in a reduced multivariate EOF space of observed SST and sea level analysis using the methodology of Xue et al 2000. The model is trained for the 1981-1998 period.
The SST is the NCEP SST analysis and the sea level is from the NCEP ocean analysis. All the data are monthly values averaged in grid boxes of 6 degrees in longitude and 2 degrees in latitude, and cover the tropical Pacific region within 19 degrees of the equator.
Forecast SST Anomaly (Degree, 3-Mon. Average)
Forecast Sea Level Anomaly (cm, 3-Mon. Average)
The full suite of Dr. Xue's model results are updated monthly and is
SPECIAL SECTION-Experimental Forecasts for Pacific Island Rainfall
The latest results from the CPC statistical
model for all predicted locations are shown below. This map-like
presentation applies only to two particular seasons (October - December
2002 and January - March 2003) of the 13 three month periods out to a year
in advance that are available from the model. The full time series
in graphs and tables are updated monthly on the internet at:
Negative numbers are forecasts for less than normal rainfall while positive numbers are forecasts for greater than normal rainfall. The size of the number (not the value of the number) indicates how accurate the forecast is expected to be, on the average, for the station at the given time of year and the forecast lead time. There are three sizes: the smallest size indicates low skill, the medium size indicates moderate skill, and the largest size indicates a relatively high skill. The value of the numbers tell how large a deviation from normal is expected. These values are in standardized units that indicate how typical (or atypical) the rainfall conditions are expected to be relative to the station’s normal climatology. For example, numbers from 0 to 25 (or 0 to -25) are small deviations, indicating conditions that would be considered typical of the climate for the station and the time of year. Deviations from 25 to 60 (or -25 to -60) are moderate deviations, indicating somewhat wetter (or drier) conditions than would be expected for the station and the time of year. Deviations of over 60 (or less than -60) are large deviations, indicating much wetter (or drier) conditions than normal for that location and time of year.
(list not complete, selected sites only)
1. Hawaii: Hilo, Kahului, Honolulu, Lihue
2. Guam: Anderson AFB, Guam WSFO
3. Johnston Island
4. Koror WSO, Palau
5. Kwajalein Atoll
6. Majuro WSO, Marshall Is.
7. FSM: Pohnpei WSO, Yap WSO, Chuuk WSO
8. Wake Island
9. Henderson, Solomon Islands
10. Luganville, Vanuatu
11. New Caledonia: Koumac, Noumea
12. Funafuti, Tuvalu
13. Fiji: Rotuma, Undu Point, Nadi
14. Hihifo, Wallis & Futuna
15. Tonga: Niuatoputapu, Vavau
16. Rarotonga, Cook Islands
17. French Polynesia: Atnona, Bora Bora, Papeete, Takaroa, Rikitea, Tubai, Rapa
ACKNOWLEDGEMENTS AND FURTHER INFORMATION
The information contained in the LOCAL VARIABILITY SUMMARIES section and elsewhere in this issue of the Pacific ENSO Update has been drawn from many sources. Further information may be obtained by contacting your local National Weather Service office, or the individuals and institutions listed below:
NOAA National Weather Service-National Centers for Environmental Prediction
(NCEP)-CLIMATE PREDICTIONS CENTER (CPC):
World Weather Building, Washington D.C. 20233
Contact CPC at 301-763-8155 for more information on the ENSO Advisory, the Long-Lead Outlook for the Hawaiian Islands, and other publications discussed in this bulletin.
NOAA National Weather Service-Pacific Region
WEATHER SERVICE FORECAST OFFICE (WSFO)
University of Hawaii at Manoa
HIG #225, 2525 Correa Rd.
Honolulu, HI 96822
Contact the WSFO at 808-973-5270 for more information on NWS-PR sources of climate information.
University of GUAM (UOG) WATER AND ENERGY RESEARCH INSTITUE (WERI):
Lower campus, University of Guam
UOG Station, Mangilao, Guam 96923
Contact M. Lander at 671-735-2685 for information on tropical cyclones and climate in the Pacific Islands.
NOAA National Weather Service-Pacific Region
WEATHER SERVICE FORECAST OFFICE (WSFO)
3232 Hueneme Road, Barrigada, Guam, 96913
Contact C. Guard at 641-472-0900 for further information on tropical cyclones and climate in the Pacific Islands.
University of Hawaii at Manoa
School of Ocean and Earth Science and Technology (SOEST)
Department of Meteorology
HIG #350, 2525 Correa Rd.
Honolulu, HI 96822
Contact Dr. T. Schroeder at 808-956-7476 for more information on hurricanes and climate in Hawaii.
PACIFIC EL NINO-SOUTHERN OSCILLATION (ENSO) APPLICATIONS CENTER:
University of Hawaii at Manoa
School of Ocean and Earth Science and Technology (SOEST)
Department of Meteorology
HIG #350, 2525 Correa Rd.
Honolulu, HI 96822
Contact R. Schneider at 808-956-2324 for more information on ENSO-related climate data for the Pacific Islands.
Contact C. Anderson at 808-956-3908 for more information on Pacific ENSO Update and applications.
For further information, please contact:
Editor, Pacific ENSO Update,
Pacific ENSO Applications Center
c/o Dept. of Meteorology, HIG Room 350
University of Hawaii - Manoa Campus
2525 Correa Road - Honolulu, HI 96822
Tel: 808-956-2324 Fax: 808-956-2877
Publication of the Pacific ENSO Update is funded in part
by Grant Number NA46GP0410 from the National Oceanic
and Atmospheric Administration (NOAA) Office of Global
Programs. The views expressed herein are those of the
author(s) and do not necessarily reflect the views of NOAA
or any of its sub-agencies.
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