1. Tropical cyclone activity
1.1 Tropical cyclones ending during the month
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Basin name abbreviations:
NWP : North-west Pacific (west of 180° E)
NEP : North-east Pacific (east of 180° E)
NAT : North Atlantic
NI : North Indian (west of Malay Peninsula)
SWI: South-west Indian (west of 90° E)
AUS: Australian (east of 90° E)
1-minute MSW: Maximum sustained wind (knots) averaged over 1
minute (JTWC Hawaii, NHC Miami, CPHC Hawaii)
10-minute MSW: Maximum sustained wind (knots) averaged over 10
minutes (JMA Japan, Southern Hemisphere RSMCs and TCWCs)
Note: Although 1-minute average winds should be stronger than
10-minute average, this may not be the case here since estimates are
obtained from different warning centres.
1.2 Tropical cyclones still active at the end of the month
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2. Forecast error statistics
The Met Office global Numerical Weather Prediction model produces a 6-day forecast every 12 hours. The performance of the model in forecasting this month's tropical cyclones is assessed below. Mean error statistics for each storm that ended during the month are presented together with a final table of statistics for all storms ending this month. Verification is performed at 24 hour intervals up to forecast time T+120. Some mean error statistics for last year's storms are included for the purposes of a comparison. The present global model has a resolution of 0.5625°x 0.375°x 50 levels. This is equivalent to a horizontal resolution of 62km x 42km at the equator.
The Met Office verification scheme identifies the centre of a tropical cyclone in the model by locating a local maximum of relative vorticity at 850hPa. This local maximum is also used in the verification of intensity. A fourth order interpolation is used to locate the centre accurately. Advisory data received in real time from various tropical cyclone warning centres are used as verifying observations of storm location.
The terms used in the statistics tables are explained below:
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All errors are measured in kilometres except where indicated.
- Observed maximum wind at least 31 knots at the verifying time.
- Forecast tropical cyclone centre equatorwards of 45 degrees.
- Forecast tropical cyclone centre relative vorticity above a critical limit for verification (1.0x10-4 per second).
- Observation within 6 hours of verifying time present for use in verification.
Track skill is defined as:- (CLIPER DPE - Model DPE) / CLIPER DPE x 100%
Positive skill indicates the model forecast is better than CLIPER.
Negative skill indicates the CLIPER forecast is better than the model.
A diagrammatic explanation of other error statistics and their sign conventions can be found in Appendix A. Full details of the TC verification scheme can be found in nwp Gazette, Vol.1, No.2, December 1994.
2.1 Individual tropical cyclone summaries
Name: GAMEDE Identifier: 15S
Basin: SOUTH-WEST
INDIAN
Start date: 21.02.2007 End
date: 02.03.2007
1-minute MSW: 105 knots
10-minute MSW: 95 knots
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* DPE for all storms in the 2005-6 season in the SWI basin
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Plot of the storm's observed track and forecasts |
Track forecast errors were above last season’s average for this storm at lead times of T+48 and greater. The model indicated a slow down in motion mid-way through the storm’s life as actually happened, but tended to push Gamede too far west into Madagascar. Despite the large track errors, skill scores against CLIPER were positive.
Name:ODETTE Identifier: -
Basin: AUSTRALIAN
(Coral Sea)
Start date: 02.03.2007 End
date: 06.03.2007
1-minute MSW: - knots 10-minute
MSW: 45 knots
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* DPE for all storms in the 2005-6 season in the AUS basin
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Plot of the storm's observed track and forecasts |
Odette was a short-lived storm and only one forecast was verified.
Name:GEORGE Identifier: 12P
Basin: AUSTRALIAN (South-east Indian)
Start date: 03.03.2007 End date: 09.03.2007
1-minute MSW: 110 knots 10-minute MSW: 105 knots
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* DPE for all storms in the 2005-6 season in the AUS basin
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Plot of the depression's observed track and forecasts |
The Met Office global model shared the same error as several other numerical models and failed to predict the sharp leftwards turn and landfall of George. This led to huge track forecast errors and negative skill scores. The error seems to be associated with the model’s failure to predict the formation of TC Jacob and its interaction with George.
Name:JACOB Identifier: 18S
Basin: AUSTRALIAN (SE Indian)
Start date: 07.03.2007 End date: 12.03.2007
1-minute MSW:75 knots 10-minute MSW: 75 knots
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* DPE for all storms in the 2005-6 season in the AUS basin
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Plot of the storm's observed track and forecasts |
The model did not predict the formation of Jacob well and dissipated the storm in some of its early forecasts too soon. However, of the forecasts verified track errors were generally low and skill scores high.
Name:INDLALA Identifier: 19S
Basin:
SOUTH-WEST INDIAN
Start date: 12.03.2007 End date: 16.03.2007
1-minute
MSW: 115 knots 10-minute MSW: 95 knots
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* DPE for all storms in the 2005-6 season in the SWI basin
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Plot of the depression's observed track and forecasts |
Track forecasts for this storm were low. However, due to exceptionally small CLIPER errors, skill scores were negative.
Name:KARA Identifier: 20S
Basin:AUSTRALIAN (SE Indian)
Start date: 25.03.2007 End date: 28.03.2007
1-minute
MSW: 80 knots 10-minute MSW: 85 knots
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* DPE for all storms in the 2005-6 season in the AUS basin
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Plot of the storm's observed track and forecasts |
Kara was fairly short-lived, but the turn of the storm towards the coast was well predicted.
Name:BECKY Identifier: 21P
Basin:AUSTRALIAN (SW Pacific)
Start date: 26.03.2007 End date: 29.03.2007
1-minute
MSW: 70 knots 10-minute MSW: 60 knots
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* DPE for all storms in the 2005-6 season in the AUS basin
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Plot of the storm's observed track and forecasts |
Becky was relatively short-lived, but track forecast errors were low and the T+24 skill score high.
2.2 Summary of all tropical cyclones
Mean error statistics for all tropical cyclones (of at least tropical storm strength) which have ended this month are shown below.
Total number of depressions ending this month: 7
Number of storms used in statistics below:7
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* DPE for all southern hemisphere storms in 2005-06 season
Comments:
This month’s statistics are dominated by TCs Gamede and George and show large track forecast errors at lead times greater than T+24. There was a modest amount of skill over CLIPER and there was a right-of-track bias in forecasts. The overall intensity tendency skill score was 18%..