Tropical cyclone activity and forecasts - December 2007
Tropical cyclone activity
| NWP | NEP | NAT | NI | SWI | AUS | Total | |
|---|---|---|---|---|---|---|---|
| Total number ending during the month | 0 | 0 | 1 | 0 | 2 | 1 | 4 |
| NWP | NEP | NAT | NI | SWI | AUS | Total | |
|---|---|---|---|---|---|---|---|
| Daman | 05P | AUS | 05 December | 09 December | 105 | 100 | |
| Olga | 17L | NAT | 11 December | 13 December | 50 | - | |
| Celina | 06S | SWI | 13 December | 21 December | 35 | 40 | |
| Dama | 07S | SWI | 18 December | 21 December | 50 | 35 |
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.
Tropical cyclones still active at the end of the month
| Name | Identifier | Basin | Start date |
|---|---|---|---|
| Melanie | 08S | AUS | 28 December |
| Elnus | 09S | SWI | 31 December |
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.
Individual tropical cyclone summaries
Name: DAMAN Identifier: 05P
Basin: AUSTRALIAN (South Pacific)
Start date: 05.12.2007 End
date: 09.12.2007
1-minute MSW: 105 knots
10-minute MSW: 100 knots
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | |
|---|---|---|---|---|---|---|
| Possibly verified | 8 | 6 | 4 | 2 | 0 | 0 |
| Detection rate (%) | 100 | 100 | 100 | 100 | **** | **** |
| Mean DX | -5 | -73 | -273 | -420 | **** | **** |
| Mean DY | 14 | 0 | 103 | 356 | **** | **** |
| Mean AT | 4 | -117 | -147 | 319 | **** | **** |
| Mean CT | -21 | -35 | -217 | -368 | **** | **** |
| Track skill (%) | **** | 60 | **** | **** | **** | **** |
| Mean DPE | 33 | 169 | 303 | 555 | **** | **** |
| 2006 DPE * | 62 | 149 | 351 | 665 | 1062 | 1533 |
| Intensity skill (%) | **** | 67 | 50 | 0 | **** | **** |
* DPE for all storms in the 2006 season in the AUS basin
 |
Plot of the storm's observed track and forecasts |
Forecasts for Daman failed to predict the sharpness of recurvature and track forecast errors were high.
Name: OLGA Identifier: 17L
Basin: NORTH ATLANTIC
Start date: 11.12.2007 End
date: 13.12.2007
1-minute MSW: 50 knots 10-minute MSW: - knots
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | |
|---|---|---|---|---|---|---|
| Possibly verified | 4 | 2 | 0 | 0 | 0 | 0 |
| Detection rate (%) | 100 | 100 | **** | **** | **** | **** |
| Mean DX | -8 | 16 | **** | **** | **** | **** |
| Mean DY | 31 | 84 | **** | **** | **** | **** |
| Mean AT | -8 | -3 | **** | **** | **** | **** |
| Mean CT | 30 | 84 | **** | **** | **** | **** |
| Mean DPE | 98 | 85 | **** | **** | **** | **** |
| 2006 DPE * | 46 | 109 | 213 | 322 | 425 | 529 |
| Intensity skill (%) | **** | 0 | **** | **** | **** | **** |
* DPE for all storms in the 2006 season in the NAT basin
 |
Plot of the storm's observed track and forecasts |
Just two forecasts were verified for this storm and track forecast errors were low.
Name: CELINA Identifier: 06S
Basin: SOUTH-WEST INDIAN
Start date: 13.12.2007 End
date: 21.12.2007
1-minute MSW: 35 knots 10-minute MSW: 40 knots
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | |
|---|---|---|---|---|---|---|
| Possibly verified | 2 | 0 | 0 | 0 | 0 | 0 |
| Detection rate (%) | 100 | **** | **** | **** | **** | **** |
| Mean DX | -36 | **** | **** | **** | **** | **** |
| Mean DY | 89 | **** | **** | **** | **** | **** |
| Mean AT | 81 | **** | **** | **** | **** | **** |
| Mean CT | 52 | **** | **** | **** | **** | **** |
| 2006-7 DPE * | 49 | 129 | 279 | 456 | 662 | 799 |
* DPE for all storms in the 2006-7 season in the SWI basin
 |
Plot of the storm's observed track and forecasts |
Celina existed as a tropical depression for a long time, but only briefly as a tropical storm. No forecasts were verified.
Name: DAMA Identifier: 07S
Basin: SOUTH-WEST INDIAN
Start date: 18.12.2007 End
date: 21.12.2007
1-minute MSW: 50 knots 10-minute MSW: 35 knots
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | |
|---|---|---|---|---|---|---|
| Possibly verified | 2 | 0 | 0 | 0 | 0 | 0 |
| Detection rate (%) | 100 | **** | **** | **** | **** | **** |
| Mean DX | -53 | **** | **** | **** | **** | **** |
| Mean DY | -50 | **** | **** | **** | **** | **** |
| Mean AT | -76 | **** | **** | **** | **** | **** |
| Mean CT | 8 | **** | **** | **** | **** | **** |
| Mean DPE | 78 | **** | **** | **** | **** | **** |
| 2006-7 DPE * | 49 | 129 | 279 | 456 | 662 | 799 |
* DPE for all storms in the 2006-7 season in the SWI basin
 |
Plot of the storm's observed track and forecasts |
Dama was only briefly a tropical storm and no forecasts were verified.
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: 4
Number of storms used in statistics below: 4
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | |
|---|---|---|---|---|---|---|
| Possibly verified | 16 | 8 | 4 | 2 | 0 | 0 |
| Detection rate (%) | 100 | 100 | 100 | 100 | **** | **** |
| Mean DX | -16 | -51 | -273 | -420 | **** | **** |
| Mean DY | 19 | 21 | 103 | 356 | **** | **** |
| Mean AT | 1 | -88 | -147 | 319 | **** | **** |
| Mean CT | 3 | -5 | -217 | -368 | **** | **** |
| Track skill (%) | **** | 60 | **** | **** | **** | **** |
| Mean DPE | 63 | 148 | 303 | 555 | **** | **** |
| 2006 DPE * | 54 | 136 | 298 | 496 | 727 | 870 |
| Intensity skill (%) | **** | 50 | 50 | 0 | **** | **** |
* DPE for all northern hemisphere storms in 2006-7 season
This month's figures were dominated by TC Daman. Track errors were above last season’s average. The overall intensity tendency skill score was 43%.
Tropical cyclone activity in the northern hemisphere during 2007
| NWP | NEP | NAT | NI | TOTAL | |
|---|---|---|---|---|---|
| Tropical Depressions | 3(4) | 4(6) | 2(0) | 0(0) | 9(10) |
| Tropical storms | 10(8) | 7(8) | 9(5) | 3(5) | 29(26) |
| Hurricanes/Typhoons | 15(15) | 4(10) | 6(5) | 3(1) | 28(31) |
| Total | 28(27) | 15(24) | 17(10) | 6(6) | 66(67) |
( ) The number in brackets indicates the figure for the 2006 season.
* NWP total includes Haiyan and Podul (no warnings by JTWC)
Summary of all Northern Hemisphere Tropical Cyclones in 2007
Mean error statistics for all northern hemisphere tropical cyclones which occurred in 2007 are shown below. Only TCs which reached tropical storm intensity at the time of a forecast are used in the statistics below.
Total number of tropical depressions which occurred: 67
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | |
|---|---|---|---|---|---|---|
| Possibly verified | 400 | 288 | 209 | 146 | 95 | 59 |
| Detection rate (%) | 100 | 100 | 100 | 100 | 99 | 93 |
| Mean DX | 5 | -11 | -29 | -59 | -131 | -126 |
| Mean DY | -1 | 10 | 4 | -36 | -91 | -56 |
| Mean AT | -6 | -26 | -24 | -35 | -119 | -138 |
| Mean CT | 5 | 6 | -21 | -45 | -76 | -31 |
| Skill (%) | **** | 33 | 50 | 56 | **** | **** |
| * 2006 Skill | **** | 30 | 41 | 44 | **** | **** |
| Mean DPE | 62 | 126 | 193 | 266 | 402 | 469 |
| 2006 DPE * | 57 | 112 | 203 | 303 | 422 | 537 |
| Intensity skill (%) | **** | 33 | 19 | 16 | 28 | -9 |
* Real time figures for all northern hemisphere storms in 2006
The total number of tropical cyclones (including tropical depressions) was similar to last year, with a slight increase in Tropical storms, but decrease in hurricanes/typhoons. Whilst the number of storms was similar to last year, the number of verifiable forecasts was much lower due to the short-lived nature of many tropical cyclones. This was particularly the case in the North Atlantic which saw above-average storm numbers, but each storm lasting little more than two days on average. Other regions saw average or below-average activity, although it was notable that unusually, two very intense tropical cyclones developed in the North Indian Ocean.
NWP 
NEP 
NAT 
NI
The charts show forecast positional errors for each basin in the northern hemisphere over the last few years. In all regions, track errors were lower than in recent seasons at the majority of lead times. The only increases in error were at T+24 in the North-West Pacific and T+24, T+48 and T+96 in the North-East Pacific. The North Atlantic saw a dramatic drop in forecast errors at all lead times, although it should be noted that there were very few verifiable forecasts at longer lead times – e.g. only one storm produced verifiable 5-day forecasts.
Error graphs for the whole of the northern hemisphere indicate that track forecast errors were the lowest recorded at all lead times except T+24, which saw a slight increase. Skill scores were the highest ever achieved at all lead times. Along track errors were slightly larger than previous seasons at longer lead times. The positive cross track errors at longer lead times seen in previous years reversed to become negative this season.
The intensity tendency skill score averaged for all forecasts was 23% in 2007. This compares for the figure of 21% for 2006.
A revised northern hemisphere summary will be issued once best track data has been collected later in the year.
Forecast Positional Errors
NWP 
NEP 
NAT 
NI 
Combined
northern hemisphere
Northern
hemisphere skill
Northern
hemisphere cross track errors
Northern
hemisphere along track errors
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