RSMC Tokyo
Activity Report
1. Introduction
1.1Functions of the Center
The area of responsibility of the Center covers tropical and subtropical waters of the western North Pacific Ocean, from the equator to 60N in latitude and from 100E to 180E in longitude. It includes marginal seas of the western North Pacific Ocean and adjacent land areas.
Major operational functions of the Center are:
-to monitor tropical cyclones (TCs) and to issue forecasts and relevant meteorological information on their track and development/decay,
-to analyze synoptic meteorological conditions that may affect movement, development and decay of TCs, and
-to disseminate the above information to the National Meteorological Services concerned in appropriate forms.
These functions are activated around the clock when a gale-force or stronger wind area associated with a tropical cyclone exists and/or is expected to exist within 24 hours in the area of responsibility (AOR). Specific conditions for the activation of the functions are as follows:
-A tropical cyclone of tropical storm (TS) intensity or higher exists in the AOR.
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-A tropical cyclone is expected to reach TS intensity or higher within 24 hours in the AOR.
-The 70% probability circle of 24-hour center position forecast or the 24-hour storm warning area of a TC is expected to reach the AOR.
In addition, the Center has non-real-time functions such as the publication of the Annual Activity Report and the Technical Review and the provision of assistance to the Members of the Typhoon Committee to improve their relevant capabilities through training activities.
1.2 History
The Regional Specialized Meteorological Center (RSMC) Tokyo-Typhoon Center with activity specialization in analysis, tracking and forecasting of TCs in the western North Pacific and the South China Sea was established in July 1989 at the Headquarters of the Japan Meteorological Agency (JMA). It is co-located at the RSMC with geographical specialization within the framework of the World Weather Watch program of the WMO. Since then, the RSMC Tokyo-Typhoon Center (hereinafter referred to as the Center) has provided the Members of the Typhoon Committee and other WMO Members with tropical cyclone forecasts and advisories. See Appendix 1 for the history of the products and services of the Center.
- Operational Analysis and Forecasting Methods
2.1 Operational Analysis and Forecasting
The Center analyzes the following parameters of a tropical cyclone (TC) on a real-time basis using various observational data, such as synopticobservations, GMS cloud imagery and radar observations. Analyses are also made for a tropical depression with maximum sustained wind at and above 28 knots (near gale).
-Center position with its precision
-Central pressure
-Maximum sustained wind (10-minute average)
-Radii of 50- and 30-knot wind areas
-Direction and speed of movement
The intensity analysis is mostly made with the Dvorak method over open waters where in-situ measurements are rarely available.
Analysis Software
RSMC has adopted a TC analysis software for operational use. The introduction of the software enables forecasters to compute an idealized pressure profile of a target TC that is a best fit to the sea-level pressure observations in the least-square sense, and hence to provide an estimate of central pressure. From the resultant profile of gradient wind speeds with respect to the distance from cyclone center, an upper bound to the maximum sustained wind can be obtained.
The Center makes the following forecasts for a TC.
at 0000, 0600, 1200, and 1800UTC
12-, 24-, 48-, and 72-hour forecasts of
-center position,
-radius of 70% probability circle of center position forecast,
-direction and speed of movement
12-, 24-, and 48-hour forecasts of
-central pressure
-maximum sustained wind
at 0300, 0900, 1500, and 2100UTC
12- and 24-hour forecasts of
-center position,
-radius of 70% probability circle of center position forecast,
-direction and speed of movement
-central pressure
-maximum sustained wind
48- and 72-hour forecasts issued 3-hours earlier are relabeled 45- and 69-hour forecasts, respectively, and attached to the 12- and 24-hour forecasts )
(Note: 12-hour forecasts are omitted in some cases, but are produced whenever necessary, e.g., in a case where TC movement is changeable)
Forecasts of TC track now heavily rely on the products of the dynamical models at JMA. Forecasts of TC intensity has been becoming increasingly dependent on the products of one of the dynamical model (TYM) at JMA, while the time extrapolation of the CI number determined with the Dvorak method is still useful, especially for short forecast ranges.
2.2 Numerical Models
The Typhoon Model (TYM) and the Global Spectral Model (GSM) are used for the prediction of track and intensity of tropical cyclones. Both models were up-graded on 1 March 2001 in expectation of producing better tropical cyclone predictions. Major features of the two models are outlined in Appendix 2. Detailed descriptions are found in the new Home Page of JMA: Operational configuration of the two models is shown in Appendix 3. Specific aspects of the performance of TYM and GSM are described in a publication by the Center (its Technical Review No. 5, March 2002).
As one of the activities under the WGNE of WMO/CAS-JSC, an intercomparison of performance in the western North Pacific tropical cyclone track prediction among several global models of major numerical weather predictions centers has been conducted by the lead of JMA. The intercomparison for a ten-year period is summarized in the latest WMO bulletin (Tsuyuki et al., 2002, July 2002 issue of WMO Bulletin, Vol. 51 No. 3).
2.2.1 Operational Schedule and Products of GSM
(a) Operational Schedule
0000 UTC: analysis and forecast up to 90 hours.
1200 UTC: analysis and forecast up to 216 hours.
(The first 90 hours of which are used for TC forecast.)
A bogus vortex is produced and implanted into the first guess field of the analysis for each tropical depression (TD) with maximum wind speed of 28 knots or higher as well as for tropical cyclones of tropical storm (TS) intensity or higher in the AOR
(b) Products for forecaster
Predictions of:
-center position
-intensity (central pressure)
-intensity (maximum sustained wind speed)
-radii of 30-knot winds in four quadrants
-radii of 50-knot winds in four quadrants
at 6-hour intervals
2.2.2Operational Schedule and Products of TYM
(a) Operational Schedule
0000, 0600, 1200, and 1800 UTC : analysis and forecast up to 84 hours.
A maximum of 2 tropical cyclones (i.e. 2 separate model runs) can be targeted at each synoptic time.
(b) Products for forecaster
Predictions of:
-center position
-intensity (central pressure)
-intensity (maximum sustained wind speed)
-radii of 30-knot winds in four quadrants
-radii of 50-knot winds in four quadrants
at 3-hour intervals
2.2.3 Improvement of Global Data Assimilation System
The data assimilation method for the Global Spectral Model (GSM) Data Assimilation System was changed from the three-dimensional multi-variate optimum interpolation method (3D-OI) to the three-dimensional variational method (3D-Var). This change is expected to lead to better performance of TC track prediction as well as general weather forecast.
2.2.4 Improvement of Tropical Cyclone Bogus Method in Typhoon Model
Two improvements were made in 2002 of the TC bogusing scheme of JMA's Typhoon Model (TYM) .
a) An upper bound (800 km) was set to the outer radius of the annular zone for blending the bogus vortex with Global Analysis in May 2002. In the previous TC bogusing scheme, the radius of the annular zone for blending the bogus TC with Global Analysis had been determined in proportion to the operationally analyzed radius of 30kt winds without any upper bound. In some cases, where the wind radius had been overestimated in the operational analysis, the annular zone had been too large, leading to a large track error.
b) The minimum value of the scale length, which characterizes the horizontal size of the bogus vortex, was increased in July 2002, in order to ameliorate the dynamical balance in the initial field for small and intense tropical cyclones. In the previous scheme, a serious dynamical imbalance had often arisen in the case of a relatively small-scale intense storm. The central portion of the bogus vortex had not been resolved with the model grid and an oscillation of central pressure with its amplitude of more than 5hPa had been seen for the first several hours of prediction.
2.3 Guidance for Operational Forecasts
2.3.1 Track Forecasts
In order to provide forecasters with track forecast guidance that works to reduce forecast errors, the Center developed a method of modifying the output of numerical prediction models. The method adjusts the model predicted track with the latest analysis available, i.e., shifts the whole track based on the positional error vector at T+6h.
2.3.2 Intensity Forecasts
The same kind of method is applied to a guidance method for intensity forecasts.
2.3.3 Sea Wave Models and a Storm Surge Model
JMA operates three sea wave models: a global wave model with 1.25-deg resolution producing 90-hour and 216-hour predictions at 0000 and 1200UTC, respectively, a Japan-area wave model with 0.5-deg resolution producing 90-hour predictions twice daily and a coastal wave model with 0.1-deg resolution producing 72-hour predictions twice daily. The former two models use prognostic differential equations expressed by wave spectra and the latter one is a diagnostic model which combines a spectrum method with a significant wave one.
JMA developed a numerical model for storm surge prediction and has been operating it since July 1, 1998. The model is a dynamical model with the horizontal resolution of 1.6km. External forcings given to the model are sea surface pressure and winds, which are estimated with the sea-level pressure distribution formula by Fujita and the translation velocity of a tropical cyclone. The storm surge prediction, therefore, highly depends on an official track and intensity forecast of the tropical cyclone. The storm surge model now covers almost the entire Japanese coasts except Hokkaido and runs four times a day to produce 24-hour predictions when a tropical cyclone is located close to or just making landfall on Japan.
2.3.4 Probability of Entering Storm-force Wind Area
JMA now calculates and issues the probability of entering the storm-force wind area of a TC in 24 hours for 29 major cities in Japan. The probability is calculated using the center position forecast probability circle and the predicted radius of 50-knot wind area. It will be enhanced in 2003 such that the probability is calculated for all the three-hour time intervals up to 48 hours ahead and for about 300 local districts for issuing meteorological warnings.
3. Verification of Forecasts
3.1 Track Forecasts
Annual means of errors of official center position forecasts are shown in Figure 4.1 in Appendix 4. Long-term trends show that the forecasts have been improved steadily. The year 2002, although the season has not ended and the verification is provisional, marked the best performance on record for all the forecast ranges. A major portion of the improvement can be attributed to the enhancement of the performance of the numerical models. Presumably the enhancement of the performance of the numerical models is mainly explained by the improvement of their initial fields by the introduction of 3-dimensional variational method into the Global and Typhoon Analyses.
3.2 Intensity Forecasts
Annual means of errors (root mean square errors RMSEs) of official intensity (central pressure and maximum sustained wind speed) forecasts are shown in Table 4.1 in Appendix 4. JMA started issuing 48-hour intensity forecasts in June 2001. The year 2002 shows nearly the same performance in 48-hour intensity forecast as the year 2001.
4. Operational Products of the Center
The Center compiles and distributes the following products and bulletins via GTS, AFTN and JMH with abbreviated headings shown in the parentheses. These are RSMC Tropical Cyclone Advisory, RSMC Guidance for Forecast, SAREP, RSMC Prognostic Reasoning and Tropical Cyclone Advisory for SIGMET. They are issued when a tropical cyclone of tropical storm (TS) intensity or higher exists and/or it is expected to affect the AOR within 24 hours.These bulletins are continually issued for a TC as long as it keeps TS intensity or higher within the AOR. Samples of these products are shown in Appendix 5.
4.1 SAREP (TCNA20/TCNA21 RJTD)
The SAREP reports a tropical cyclone analysis based on the Dvorak method, which estimates the tropical cyclone intensity with GMS imagery. It contains the center position of a tropical cyclone, accuracy of the center position fix, mean diameter of the cloud system, CI-number, apparent change in intensity in the last 24 hours, direction and speed of movement. These analyses are produced using GMS imagery obtained at 00, 03, 06, 09, 12, 15, 18 and 21 UTC. SAREP is issued a half to one hour after the observation with the headings of TCNA20 RJTD for 03,09,15,21 UTC and TCNA21 RJTD for 00, 06, 12 and 18 UTC.
4.2 RSMC Tropical Cyclone Advisory (WTPQ20-25 RJTD)
The RSMC Tropical Cyclone Advisory reports JMA's official analysis and forecast of a tropical cyclone. The analysis part contains center position of a tropical cyclone, accuracy of the center position fix, direction and speed of movement, central pressure, maximum sustained wind speed (ten-minute average), radii of 50- and 30-knot wind areas. The forecast part contains center position and radius of the center position forecast probability circle, direction and speed of movement, central pressure, maximum sustained wind speed (ten-minute average) for 24- and 48-hour forecasts. The center position forecast probability circle defines a circular range within which the center of a tropical cyclone is expected to reach with a probability of 70% at each time of validation.
The Center increased frequency of issuing the RSMC Tropical Cyclone Advisory (WTPQ20-25 RJTD) from every 6 hours to every 3 hours on 10 July 2002.
4.3 RSMC Guidance for Forecast (FXPQ20-25 RJTD)
The RSMC Guidance for Forecast reports the numerical predictions by GSM and TYM. GSM runs twice daily with global analyses given at 0000 and 1200 UTC as its initial fields. The model produces 6-hourly prognoses of a tropical cyclone up to T+90 hours. TYM runs four times a day with initial analyses at 0000, 0600, 1200, and 1800UTC. The model produces 6-hourly prognoses up to T+84hours. The RSMC Guidance for Forecast includes center position of a tropical cyclone, central pressure, and maximum sustained wind speed. Predictions of central pressure and maximum sustained wind speed are given as deviations from those at the initial time.
4.4 RSMC Prognostic Reasoning (WTPQ30-35 RJTD)
The RSMC Prognostic Reasoning is issued to provide a brief reasoning for a tropical cyclone forecast. It is issued normally at 0000 and 0600UTC following the issuance of RSMC Tropical Cyclone Advisory. In the bulletin, general comments on the forecasting method, synoptic situation, such as behavior of a subtropical high pressure (anti-cyclone), movement and intensity of the tropical cyclone, and some relevant remarks are made in plain language.
4.5 Prognostic Charts of 850 hPa/200hPa Streamline (FUXT852/202, FUXT854/204 on JMH)
The 24- and 48-hour prognostic charts of 850hPa/200hPa streamline are broadcast via JMH with the headers of FUXT852/202 and FUXT854/204, respectively. These prognoses are produced based on GSM forecasts at 0000 and 1200UTC for the fixed area spanning from 20S to 60N in latitude and from 80E to 160W in longitude.
4.6 Tropical Cyclone Advisory for SIGMET (FXPQ30-35 RJTD)
The Center was designated as one of the Tropical Cyclone Advisory Centers (TCAC) at the third Asia/Pacific Regional Air Navigation Meeting (Bangkok, 19 April - 7 May 1993) of International Civil Aviation Organization (ICAO). In preparation for SIGMET, the Center disseminates the Tropical Cyclone Advisory for SIGMET to Meteorological Watch Offices (MWOs) concerned. It contains analysis and 12- and 24-hour forecasts of center position, central pressure, maximum sustained wind, and direction and speed of movement. Its format will be changed on 1 January 2003 in accordance with the approval of the revised format at the meeting of ICAO Council in Montreal in March 2001.
4.7 RSMC Tropical Cyclone Best Track (AXPQ20 RJTD)
The RSMC Tropical Cyclone Best Track provides post-analysis of tropical cyclones. It contains the center position, central pressure, maximum sustained wind speed, and 30-kt and 50-kt wind radii. The Best Track for a tropical cyclone is distributed generally one and half a month after the termination of issuance of RSMC bulletins for the tropical cyclone mentioned above.
4.8Change of Server for RSMC Tropical Cyclone Advisory from DDB to JMA Home Page
In compliance with the request of the forty-ninth session of the Executive Council of WMO and the thirtieth session of the Typhoon Committee, RSMC Tokyo-Typhoon Center established Internet access to RSMC tropical cyclone advisories in March 1999 to provide the international media with basic information on tropical cyclones. The advisories now include the latest analysis on a tropical cyclone in the western North Pacific and track forecasts up to 72 hours and intensity forecasts up to 48 hours. They had been available on the WMO-Distributed Data Bases (DDBs) Server operated by JMA until August 2002, when they were moved from the DDB Server to JMA's Home Page, which was put into operation in 8 August 2002:
4.9 RSMC Data Serving System
JMA examined the feasibility of distributing data and products prepared by RSMC Tokyo - Typhoon Center to the Members of the ESCAP/WMO Typhoon Committee via GMS. However, it could not be realized due to financial and technological difficulties until the next-generation satellite (MTSAT) is launched.
As a provisional measure, JMA established the RSMC Data Serving System (RSMC DSS) as an activity of the RSMC Tokyo Typhoon Center in March 1995. The RSMC DSS has provided GPV products and observational data to the Members through international public telecommunication networks such as the Internet and Integrated Services Digital Network (ISDN). In April 2002, JMA upgraded the RSMC DSS. The new RSMC DSS provides better service to the Typhoon Committee Members by enhancing GPV products and increasing security and stability of operation for meeting the requirements of the Members. An explanation of the system configuration of the RSMC DSS is given in Appendix 6.
4.10 Numerical Tropical Cyclone Prediction Web Site
At the 34th Session of the ESCAP/WMO Typhoon Committee in Honolulu from 28 November to 4 December 2001, JMA presented its intention of establishing a web site, which would show numerical tropical cyclone predictions provided by major NWP centers for use in tropical cyclone forecasting and warning by the meteorological / hydrometeorological organizations of the Member countries / regions of the ESCAP/WMO Typhoon Committee as one of the guidance products. That was welcomed and approved by the Committee. In response to JMA's report on this plan in relation to the Tropical Meteorology Research Program (TMRP), the WMO/CAS recommended at its 13th Session in Oslo from 12 to 20 February 2002 that all NWP centers should provide their prediction fields to JMA to support the implementation of this plan of "Numerical Tropical Cyclone Prediction Web Site". The web site is believed to contribute to improving tropical cyclone forecasts and warnings issued by the meteorological / hydrometeorological organizations of the Member countries / regions of the ESCAP/WMO Typhoon Committee, by providing guidance of high performance.