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 Analysissatellite observations (Dvorak Method)surface observationsradar observations (only position)

2. TC ForecastingNWP modelsPersistence (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 intensitysatellite observationssurface observationsradar 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 MTSATMTSA

T

TC Analysis

Observations such as SYNOP/SHIP/BUOY

TC Analysis

Naha

Radar image

TC Analysis

Satellite image (Dvorak method)cloud

patternintensity

TC Analysis

01)(

rr

PPrP

0

Exponential ordinate

= Takahashi’s diagramNormal 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 (PA) and distance from the TC center (rA) 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 PCN.

PC

PA

B

C

PB

rC rA

rB

A

PCN

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 modelsDeterministic model (GSM)Ensemble system (TEPS)Consensus method (average of various models)Multi ensemble system PersistenceNote:valid only for short-term forecastsmall scale oscillations leads to wrong

interpretations. 

Models Forecast Range

Global ModelGSM TL959 L60about 20 km in horizontal,

60 layers

FT= 84h (00,06,18UTC)FT=216h (12 UTC)

Mesoscale Model

MSMabout 5 km in horizontal, 50 layers

FT=15h (00, 06, 12, 18UTC)FT=33h (03, 09, 15, 21UTC)

One-week EPSGSM TL319 L60 M51about 60km in horizontal, 60 layers

FT=216h (12UTC)

Typhoon EPSGSM TL319 L60 M11about 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≦10kt

10kt<V ≦30kt

30kt<V

24NW (260-359) 70 75

130Other (360-259) 85 85

48NW (260-359) 110 140

210Other (360-259) 160 180

72NW (260-359) 160 210

325Other (360-259) 220 250

Unit: nm

NW

other

PC radius depends on forecasted TC movement based on the verification of TC track forecast in 2004 to 2007.

2. Radius of probability circle

TC forecasting (track)

PC radius depends on ensemble spread of TEPS

based on verification of track forecasts in 2007-2008.

2. 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) (2007-2008)

Ensemble spread

TC forecasting (track)

Our verification result says that the radius of 70% probability circle enlarges in proportion to ensemble spread.

FT Group A Group B Group C

96 200 280 425

120 250 375 500

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

AG G G

G

GSM prediction

Analysis

MM M M

M

termination of adjustment (FT=36)

Initial intensity adjustment

present forecast time

M

GG

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

Cen

tral P

ressu

re (

hP

a)

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=48 FT=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

End