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| Forecasting encompasses a wide range of meteorological information such as warnings and advisories in addition to forecasts themselves. Its objective is to meet the comprehensive need to protect life and property and to enhance national socio-economic activity in various groups including the general public, industry and the transportation sector. |
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If hazardous weather conditions are expected, JMA delivers a variety of plain messages including warnings, advisories and bulletins to the general public and disaster prevention authorities so that appropriate measures can be taken to mitigate possible hazards. These messages are issued by Local Meteorological Observatories (LMOs) to their respective prefectures. Warnings for each municipality in the prefecture are issued when weather conditions are expected to be catastrophic and meet the warning criteria, while advisories are issued when conditions are expected to be disastrous and meet advisory criteria but remain below the warning criteria. Bulletins provide information to supplement warnings and advisories. They are also issued by District Meteorological Observatories (DMOs) or JMA Headquarters according to the scale or severity of the related disturbance, and include information not only on severe weather but also on possible disasters. For example, sediment disaster bulletins are issued jointly with municipalities in particular when sediment-related disasters caused by heavy rain are expected with a high possibility in the next few hours. Serious damage caused by severe storms including tornadoes in 2006 induced requirements for alerts for hazardous winds. To address this requirement, JMA started to issue the “Tornado Watch” from March 2008 based on the discussion in advisory meetings. All such information is delivered to the public through the media and directly to disaster prevention authorities from JMA Headquarters and/or DMOs. |
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Meteorological warnings/advisories issued by JMA |
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Warnings |
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Advisories |
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| JMA is also responsible for providing flood forecasting services, which are performed in collaboration with central and local government agencies. These services include flood warnings and advisories covering 407 rivers (as of March 2011) throughout the country that have been designated by the aforementioned agencies as potential flood-disaster rivers. Flood forecasting systems for 289 rivers out of 407 are managed jointly by JMA and the Water and Disaster Management Bureau of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), and 118 jointly by JMA and civil engineering bureaus of prefectural governments. |
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A Very Short-range Forecast of Precipitation is issued twice an hour to predict one-hour precipitation amounts for the next six hours with a spatial resolution of 1 km. This forecast is derived from a combination of Mesoscale Model (MSM) predictions and the extrapolation of Radar/Raingauge-Analyzed Precipitation data, which is radar-observed precipitation calibrated with the in-situ rain gauges of AMeDAS, the Water and Disaster Management Bureau, the Road Bureau and local governments. The Precipitation Nowcast provides precipitation intensity forecasts with a spatial resolution of 1 km up to one hour ahead for disaster prevention activities in the event of swiftly growing convections. It is issued every 5 minutes within 3 minutes of every 5-minute radar observation. In addition, JMA started to issue the Thunder Nowcast and the Hazardous Wind Potential Nowcast from May 2010. The Thunder Nowcast predicts the activities of thunder and lightning strikes up to one hour ahead, while the Hazardous Wind Potential Nowcast predicts the probabilities of hazardous wind such as a tornado up to one hour ahead. These two Nowcasts are issued every 10 minutes. |
 Very Short-range Forecast of Precipitation |
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Daily forecasts in plain text form for the same day, the next day and the day after are issued three times a day at 0500, 1100 and 1700 Japan Standard Time (JST) for a total of forecast blocks across the country. These daily forecasts contain information about weather, winds, coastal ocean waves, maximum/minimum temperatures and probabilities of precipitation. |
 Daily Forecast |
 Area Distribution Forecast |
In addition to forecasts in plain text, JMA also provides versions in graphic form such as Area Distribution Forecasts and Time Sequence Forecasts. Area Distribution Forecasts show the spatial distribution of weather, precipitation and temperature for the whole country with a spatial resolution of 20 km x 20 km. |
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Time Sequence Forecasts predict weather, temperature and wind speed/direction at three-hour intervals for 142 forecast blocks across the country. Both forecasts are issued at the same time as daily forecasts. |
 Time Sequence Forecast |
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One-week Forecasts cover a seven-day period starting from the day after the forecast is issued. They are put out daily at 1100 and 1700 JST to provide day-to-day predictions of weather, precipitation probability, maximum/minimum temperatures and reliability for prefectural areas of the country. Ensemble prediction techniques are employed as the main basis of the One-week Forecast, and have contributed much to the improvement of its accuracy. |
| In Long-range Forecasts, weather outlooks for the next one to several months are provided. These outlooks offer a prognosis on average temperature, precipitation, sunshine and snowfall in the three categories of above normal, near normal and below normal. Ensemble prediction techniques play an increasingly important role in long-range forecasting. Early Warning Information on Extreme Weather is issued every Tuesday and Friday when a high probability (30% or more) of very high or very low seven-day average temperatures is predicted in the week starting from five to eight days ahead of the date of announcement. |  |
 Five-day track forecast |
Tropical cyclones (TCs) can cause serious damage to various countries every year, and accurately predicting their locations and intensities is a vital challenge for JMA. The Agency categorizes TCs as shown in the following table. JMA monitors TC activity in the western North Pacific and the South China Sea, and issues TC advisories every three hours to provide related information including analysis and forecasting of location, intensity and movement up to three days ahead. When a TC moves onshore or is in the vicinity of Japan and is expected to have an impact on the country, analysis is issued every hour in order to advise the public of possible impending disasters. JMA also started issuing five-day track forecasts in 2009 based mainly on its Typhoon Ensemble Prediction System. To assist local governments in their disaster prevention activities, information on the three-hourly probability of winds measuring 50 knots or greater is issued when the likelihood is expected to exceed 0.5 percent within three days from each of 375 subdivisions all over the country. |
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Categorization of TCs in the western North Pacific |
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For the dissemination of forecasts and warnings, JMA maintains a telephone auto-answering service for the public and direct communication links between meteorological offices and central/local governments as well as the media.
The Agency also actively introduces new information technologies into its meteorological information services.
One example of this is the high-speed communications network called the Information Network for Disaster Prevention (INDiP), which enables effective and rapid dissemination of information in both text and graphic form.
INDiP connects individual LMOs/DMOs with JMA Headquarters to complement the traditionally established communication network for more user-friendly tailored provision of meteorological information - in particular warnings and advisories - directly and individually to disaster prevention authorities in individual prefectures, towns/cities and the media. Information for maritime users is transmitted by the JMA radio facsimile broadcast (JMH) service operated by JMA and fishery radio communications. It is also disseminated within the framework of the Global Maritime Distress and Safety System (GMDSS), i.e. via the NAVTEX broadcast service of the Japan Coast Guard for seas in the vicinity of Japan, and via the Safety-Net broadcast service for ships in the high seas through the maritime satellite INMARSAT. Nowadays, the Internet plays a vital role for JMA in the dissemination of wide-ranging meteorological information not only on forecasts but also on historical and current observational data - including those of other organizations - to the public. |
 Image of information flow to users through INDiP |
