Application to Heavy Rainfall

9 th THORPEX GIFS-TIGGE Working Group meeting Geneva, WMO Headquarters 31 August – 2 September, 2011 経田 正幸 KYOUDA Masayuki Numerical Prediction Division, Japan Meteorological Agency

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/

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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

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Expected in step with forecast operation’s plan

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To increase the resolution of the both EPSs’ model from TL319L60 to TL479L100

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To conduct One-week EPS from once a day to twice a day although the forecast ensemble size is reduced by about half

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To increase the ensemble size of Typhoon EPS from 11 to 25

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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

Update cycle, now and in the future

6-hourly update products up to 132 hours ahead

Plan to increase the ensemble size up to 25

12UTC 18UTC 00UTC 06UTC 12UTC Daily update products up to 9 days ahead

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

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)

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

Black solid line : Observed track Weather Chart : at 00 UTC on 6 th September

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Heavy rainfall

associated with Typhoon Fitow 3-day accumulated precipitation 烏川 Red and blue lines represent to issue flood warning and no warning , respectively.

相模川 入 間 川 多摩川 荒 川 651mm 690mm 683mm 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.

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Typhoon track forecasts of Typhoon Fitow before recurvature

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

Ensemble forecast up to 9 days ahead 3-Day Track Forecast in Typhoon Bulletins at 00UTC on 3 September 6日09時予報円 5日09時予報円 4日09時予報円 3日09時 2日09時 9月1日09時 Initial time is 12UTC 2 September.

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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.

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Worst-case scenario (1)

Initial time is 12UTC 2 September.

Representative track up to 6 days ahead

Western track with landfall 13

Worst-case scenario (2)

Initial time is 12UTC 3 September.

Representative track up to 5 days ahead

Western track with landfall 14

Model Output and Its Calibration

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Model output and its calibration

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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

Ensemble TC track up to 4 days ahead One-day rainfall amount Based on rain gauge data during19 th July 2011 Initial time is 12UTC 18 July 2011.

The analyzed TC central pressure was 980 hPa and an analyzed maximum wind speed near TC center was 80 kt. In Umaji Village of Kochi Prefecture, 851.5 mm of rainfall fell on 19 th July (local time), ranking high in Japan’s one-day precipitation.

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Calibrated precipitation

Calibrated data Raw data (control run of EPS) Three-hour accumulated rainfall from 21UTC 18 th July 2011 Underestimation of antecedent rainfall amount over the mountain regions was calibrated due to orographic effect.

Observed gridded data used in the calibration

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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, 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 Frequency bias correction forcing Blue : EPS model output Red : Rain gauge

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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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