Application to Heavy Rainfall

経田　正幸KYOUDA Masayuki

Numerical Prediction Division, Japan Meteorological Agency

9th THORPEX GIFS-TIGGE Working Group meetingGeneva, WMO Headquarters

31 August – 2 September, 2011

Contents• Information for severe weather preparation at

JMA– Early warning information– EPS product

• TC-related heavy rainfall– Case study – Typhoon Fitow (T0709)

• Model output and its calibration– Calibrated precipitation– Calibration method

• Conclusion and suggestion

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Information for Severe Weather Preparation at JMA

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Information for Severe Weather Preparation

• Warning, advisory and bulletin services for severe weather– 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.

– Bulletins provide information to supplement warnings and advisories.

• Early warning information– Five-day track forecast in Typhoon bulletins

http://www.jma.go.jp/en/typh/typh5.html– Storm, heavy rain, and high waves for the next few days in

bulletin services– Extreme weather as a kind of seasonal forecast

Issued every Tuesday and Friday when a high probability (30% or more) of very high or very low seven-day averaged temperature is predicted in the week starting from five to eight days ahead of the date of announcement

http://www.jma.go.jp/en/soukei/ 4

EPS product for early warning information

• Guidance for early warning information– Currently based on JMA EPS

• It is important to update on schedule.• Our own EPS product is easy to work especially for operational use.

– Limited use of Multi-center/TIGGE products• Others’ EPS/NWPS outputs are used for reference.• Multi-center’s and ECMWF-EPS’s track are used in TC warning process.• Ensemble TC tracks are available at the Numerical Typhoon Prediction

Web site operated by RSMC Tokyo – Typhoon Center in JMA.

• EPS plan in the near future and the next– Expected in step with forecast operation’s plan

• To increase the resolution of the both EPSs’ model from TL319L60 to TL479L100• To conduct One-week EPS from once a day to twice a day although the forecast

ensemble size is reduced by about half• To increase the ensemble size of Typhoon EPS from 11 to 25• To extend the forecast range of One-week EPS up to two weeks• To introduce “Reforecasting”

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JMA Numerical Typhoon Prediction Web site- for the NMHSs of ESCAP/WMO Typhoon Committee

Members -

Ensemble TC tracks are available on the Numerical Typhoon Prediction Web site.

•Multi-center TC tracks•TC tracks derived from Typhoon EPS

6-hourly update products up to 132 hours aheadPlan to increase the ensemble size up to 25

Daily update productsup to 9 days ahead

Plan to conduct the EPS twice a day although the ensemble size is cut

Update cycle, now and in the future

12UTC 18UTC 00UTC 06UTC 12UTC

New and timely EPS products are now available in TC warning process.

TC-related Heavy Rainfall

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Case study - Typhoon Fitow (T0709)

Black solid line : Observed track

Weather Chart :

at 00 UTC on 6th September

Typhoon Fitow made landfall in Honshu, the main island of Japan, at about 15UTC on 6th September.

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3-day accumulated precipitation

683mm651mm

690mm

荒川

多摩川

烏川

入間川

相模川

Heavy rainfall associated with Typhoon Fitow

The 3-day accumulated rainfall in mountain region located in the western part of Tokyo exceeded 500 mm and the water level of the Tama River running through Tokyo Metropolitan area exceeded dangerous level.

Red and blue lines represent to issue flood warning and no warning, respectively.

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Initial time is 12UTC 2 September.

Ensemble forecastup to 9 days ahead

9 月 1 日 09 時2 日 09 時

3 日 09 時4 日 09 時予報円

5 日 09 時予報円

6 日 09 時予報円

3-Day Track Forecastin Typhoon Bulletins

at 00UTCon 3 September

The landfall probability on Japan depended on the timing of recurvature.

Typhoon track forecasts of Typhoon Fitow before recurvature

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Plume diagram for an upriver district

Initial time is 12UTC 2 September.

In order to explore the use of medium-range NWP output to TC forecasting, it is essential to have an accurate grasp of forecast uncertainties of high-impact weather events controlled by the Typhoon motion, especially whether or not Typhoon will approach. 12

Worst-case scenario (1)Initial time is 12UTC 2 September.

Western trackwith landfall

Representative track up to 6 days ahead

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Worst-case scenario (2)Initial time is 12UTC 3 September.

Western trackwith landfall

Representative track up to 5 days ahead

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Model Output and Its Calibration

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Model output and its calibration

• Operational global EPS/NWP model– Not easy to predict precious amounts or even

the order of strong rainfalls• Underestimation of orographic rainfall (ex. Fitow)

• Statistical post-processing– employed routinely to reduce the systematic

errors of JMA NWP model• Calibration is essential to detect whether the forecasted

rainfall amount exceeds warning level or not, although the observed data are limited.

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Typhoon Ma-on bringing heavy rainfall

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Initial time is 12UTC 18 July 2011.

Ensemble TC track up to 4 days ahead

Based on rain gauge data during19th July 2011

In Umaji Village of Kochi Prefecture, 851.5 mm of rainfall

fell on 19th July (local time), ranking high in Japan’s one-day

precipitation.

One-day rainfall amount

The analyzed TC central pressure was 980 hPa and an analyzed

maximum wind speed near TC center was 80 kt.

Calibrated precipitationCalibrated data

Observed gridded data used in the calibration

Three-hour accumulated rainfall from 21UTC 18th July 2011

Underestimation of antecedent rainfall amount over the mountain regions was calibrated due to orographic effect.

Raw data (control run of EPS)

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Calibration method

• Kalman filter– The predictand is “Radar/Raingauge-Analyzed Precipitation”

data which are covered with the Japanese Islands and its surrounding sea area.

– The KF output has a tendency of lower frequency of forecasting severe weather events,

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such as heavy rainfall, than the actual.

• Frequency bias correction– The scheme is applied to

compensate the frequency bias of the KF output. Cumulative frequency

distribution of 7-day accumulated precipitation at Tokyo for July 2002 to June 2003

Blue : EPS model outputRed : Rain gauge

Frequency bias correction forcing

Conclusion and suggestion• JMA makes some guidance based on its own operational

EPS in the early warning operation.– The use and development of Multi-center/TIGGE products are

limited, but Multi-center’s track are used in TC warning process.

• Heavy rainfall forecasting associated with TC is strongly depend on the uncertainty of the TC motion.

– Statistical post-processing is useful to reduce the systematic errors in the operational global EPS model to heavy rainfall.

• To exchange gridded data for ensemble precipitation is expected in the TIGGE-FDP activity.– The rule of its exchange should be clear.

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Thank you for your kind attention.

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