Forecasting Tropical cyclones Regional Training Workshop on Severe Weather Forecasting and Warning Services (Macao, China, 9 April 2013)

Contents 1.Outline of TC forecasting process 2.TC Analysis 3.TC Forecasting 4.Verification of TC forecast and models

Outline of TC forecasting process Reanalysis Operational process Forecast products Best track Forecast Models Observations SYNOP,SHIP Radar Satellite, etc. Verification Forecasting Analysis

Outline of TC forecasting process Operational TC analysis and Forecasting 1. TC Analysis  satellite observations (Dvorak Method)  surface observations  radar observations (only position) 2. TC Forecasting  NWP models  Persistence (for very short-term forecast)

Contents 1.Outline of TC forecasting process 2.TC Analysis 3.TC Forecasting 4.Verification of TC forecast and models

TC Analysis Analysis of current position and intensity  satellite observations  surface observations  radar observations (position only) TC analysis is important for TC forecasting. With a wrong TC analysis of current position and intensity, TC forecast will be wrong even if the NWP model performance is excellent.

TC Analysis microwave image (35GHz & 85GHz) available when satellites hit a cyclone GCOM-W1 From JAXA webpage DMSP Series From NASA webpage TRMM From JAXA webpage IR & VIS image provided every 30 min. by MTSAT MTSAT

TC Analysis Observations such as SYNOP/SHIP/BUOY

TC Analysis Naha Radar image

TC Analysis Satellite image (Dvorak method) cloud pattern intensity

TC Analysis 0 Exponential ordinate = Takahashi ’ s diagram Normal ordinate Estimate of pressure profile of a tropical cyclone

TC Analysis Estimate of pressure profile of a tropical cyclone (0) This method is available if you can determine TC Center accurately. (1) Measure the distance from TC Center to SYNOP data A on the weather map. (2) Plot the point A which show the observed pressure (P A ) and distance from the TC center (r A ) on the pressure profile chart. (3) Same processes (1) & (2), plot B, C… (4) Draw a linear regression line on the pressure profile chart, then extrapolate the line to the TC center for estimating P CN. PCPC PAPA B C PBPB rCrC rArA rBrB A P CN

TC Analysis Estimate of 30-kt/50-kt wind area

Contents 1.Outline of TC forecasting process 2.TC Analysis 3.TC Forecasting 4.Verification of TC forecast and models

TC Forecasting Forecasting track and intensity Based on NWP models  Deterministic model (GSM)  Ensemble system (TEPS)  Consensus method (average of various models)  Multi ensemble system Persistence Note: valid only for short-term forecast small scale oscillations leads to wrong interpretations.

Models Forecast Range Global Model GSM T L 959 L60 about 20 km in horizontal, 60 layers FT= 84h (00,06,18UTC) FT=216h (12 UTC) Mesoscale Model MSM about 5 km in horizontal, 50 layers FT=15h (00, 06, 12, 18UTC) FT=33h (03, 09, 15, 21UTC) One-week EPS GSM T L 319 L60 M51 about 60km in horizontal, 60 layers FT=216h (12UTC) Typhoon EPS GSM T L 319 L60 M11 about 60km in horizontal, 60 layers FT=132h (00, 06, 12, 18UTC) medium range forecast short range forecast one-week forecast tropical cyclone forecast JMA NWP models

NWP Model outputs 3-day forecast 5-day track forecast TC forecasting based on NWP models

TC forecasting (track) Track forecast 1.Center position forecast 2.Radius of probability circle

TC forecasting (track) 1. Center position forecast main: GSM and TEPS reference: One-Week EPS, ECMWF, ECMWF EPS

TC forecasting (track) 2. Radius of probability circle (PC) PC shows uncertainty of track forecast. radius of PC is based on verification of recent track forecast. PC decision method is different between 72-hour forecast and 120-hour forecast.

TC forecasting (track) (1) 24, 48 and 72-hour forecast FT speed direction V ≦ 10kt10kt<V ≦ 30kt 30kt<V 24 NW ( ) Other ( )85 48 NW ( ) Other ( ) NW ( ) Other ( ) Unit: nm NW other PC radius depends on forecasted TC movement based on the verification of TC track forecast in 2004 to Radius of probability circle

TC forecasting (track) PC radius depends on ensemble spread of TEPS based on verification of track forecasts in Radius of probability circle (2) 96 and 120-hour forecast Tracks of TEPS members Pink track: ensemble mean track Black track: GSM track 6-hourly accumulated ensemble spread (km) ( ) Ensemble spread

TC forecasting (track) Our verification result says that the radius of 70% probability circle enlarges in proportion to ensemble spread. FTGroup AGroup BGroup C Unit: nautical mile 2. Radius of probability circle (2) 96 and 120-hour forecast

TC forecasting (Intensity) Intensity forecast 1.Central pressure (CP) 2.Maximum sustained wind (MSW) 3.Peak gust 4.Storm warning area

Operational TC forecast Model output and the guidance Time Central Pressure A A A A G G G G GSM prediction Analysis M M M M M termination of adjustment (FT=36) Initial intensity adjustment present forecast time M G G M GSM guidance G G 1. Central Pressure(CP)

Operational TC forecast Statistical development curve 1. Central Pressure (CP)

Operational TC forecast 2. & 3. Forecast of MSW & peak gust MSW conversion from CP Peak gust MSW x 1.4 CP MSW Statistical method

Operational TC forecast 4. Forecast of Storm warning area 50-kt wind radius (converted from CP) + PC radius Central Pressure (hPa) 50kt wind radius (NM) Standard Large Small CP 50kt-wind radius Storm Warning Area 50-kt wind radius PC radius Statistical method

Operational TC forecast 4. Forecast of Storm warning area Developing stage Mature stage

Contents 1.Outline of TC forecasting process 2.TC Analysis 3.TC Forecasting 4.Verification of TC forecast and models

Verification of TC forecast and models Position errors of track forecasts in 2011

Verification of TC forecast and models Position errors of GSM in 2011

Verification of TC forecast and models FT=48FT=72 Position errors of GSM in 2011 direction of movement

Verification of TC forecast and models Intensity errors of GSM in 2011 Developing stage develop more slowly than analysis Weakening stage development persists in many cases

Verification of TC forecast and models Position errors of TEPS in 2011

Verification of TC forecast and models example of model outputs: Nock-ten (1108) 26 Jul, 12UTC Initial

Verification of TC forecast and models example of track forecast: Nock-ten (1108) 26 Jul, 18UTC Initial

Verification of TC forecast and models example of model outputs: Nanmadol (1111) 24 Aug, 12UTC Initial

Verification of TC forecast and models example of track forecast : Nanmadol (1111) 24 Aug, 18UTC Initial

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