1. Typhoon (Tropical Cyclone) Information
Digital Typhoon provides typhoon-related data based on our own viewpoint, but critical decisions should be made on reliable typhoon (tropical cyclone) information. Hence we recommend the following two sites as reliable information sources and provide links in Typhoon News Weblog. Comparison of information from two sources is like getting a second opinion on typhoon forecast.
Japan Meteorological Agency
Typhoon information produced by Japan Meteorological Agency (JMA) is the "official" typhoon information in Japan. Information is updated every three hours under normal operation, but it is updated every hour when typhoons approach to Japan (usually within 300km). All typhoon information provided from weather service companies in Japan is based on JMA, and information from our website is also based on JMA, such as latest information at Digital Typhoon and typhoon forecast at Typhoon Track Forecast (on Google Maps). In April 2009, JMA extended the forecast period to 120 hours (5 days).
Joint Typhoon Warning Center
Typhoon information produced by Joint Typhoon Warning Center (JTWC) located in Hawaii, USA. This information is intended for use by U.S. government agencies, but is accessible from the general public. The information is updated every six hours. Only maximum sustained wind is expressed, while central pressure is not, because the data for central pressures is rarely measured for tropical cyclones.
Due to the increased access to the website, the website cannot be accessed sometimes, but even during those cases, the track chart of each typhoon can be accessed directly. Then, if you cannot move to the chart from the top page, please visit the article of each typhoon in typhoon news weblog, and move to the chart directly from there.
Notice on Maximum Sustained Wind
The value of maximum sustained wind is different between JMA and JTWC, and in most cases, the value of JTWC is higher than that of JMA. The primary reason is difference in the definition of maximum sustained wind -- namely 1 minute mean in the U.S., while 10 minutes mean in Japan. In general, the 10 minute mean wind speed is 0.88 times of 1 minute mean wind speed. Another aspect is that different methods are used for estimating maximum sustained wind from observation.
2. Notice on Typhoon Numbers
Typhoon numbers are typhoon names after number-based conventions, and the counter starts to increase from the beginning of the typhoon season in January. Japan Meteorological Agency (JMA) increases the typhoon number from Typhoon No.1 on the birth of a new typhoon. Joint Typhoon Warning Center (JTWC) also increases the typhoon number from 01W on the birth of a new typhoon. It is natural to assume that these two numbers are always identical, but in fact it is not always true. What is the reason?
This inconsistency originates in independent decision making on the birth of the typhoon made by JMA and JTWC. Those numbers started to be different when JMA acknowledges the birth of the typhoon while JTWC does not, and vice versa. Before 2000, this inconsistency also caused the birth of no-name typhoons. The judgment of the birth of the typhoon is fully dependent on the decision making of experts, so we cannot avoid the difference of opinions.
This inconsistency occurs not only between JMA and JTWC but also among meteorological agencies of other countries. For example, Typhoon 200413 in Japan was Typhoon 200414 in China, and this is also caused by the same reason. If you compare typhoon information issued from multiple countries, please check the international typhoon number (Asian names of typhoons) or the central position, and be careful not to mix up typhoons.
3. List of Typhoon Information
Access Methods Other Than This Website
Digital Typhoon provides access methods to typhoon information other than this website as follows.
Typhoon Information From Outside of Japan