Tropical cyclone forecast verification - northern hemisphere 2010

A summary of tropical cyclone activity in the Northern Hemisphere for the 2010 season together with an assessment of the performance of the Met Office global model in predicting the tracks of these tropical cyclones.

1. Introduction

A summary of tropical cyclone activity in the Northern Hemisphere for the 2010 season is presented below together with an assessment of the performance of the Met Office global model in predicting the tracks of these tropical cyclones.

Tropical cyclones are experienced in the North Pacific, North Atlantic and North Indian Oceans and nearby tropical seas. For the purpose of tropical cyclone verification the northern hemisphere is divided in to four basins; the North-West Pacific (west of 180°E to the Malay Peninsula), the North-East Pacific (east of 180°E), the North Atlantic and the North Indian Ocean (west of the Malay Peninsula). Mean error statistics for each basin are presented together with a table of statistics for the whole Northern Hemisphere. Verification is performed at 12-hour intervals up to forecast time T+144, although statistics are only presented at 24-hour intervals in this report. The global model resolution in operation during the season was 0.3515625° x 0.234375° x 70 levels. This is equivalent to a horizontal resolution of 39km x 26km at the equator.

An explanation of error statistics and their sign conventions.

Advisory positions received in real time from RSMC Tokyo, JTWC Hawaii, NHC Miami and CPHC Honolulu are used as verifying observations of storm location. Best track data from these centres will be obtained once they become available. Past experience shows that use of best track rather than real time data usually only makes minor differences to seasonal error statistics. Some mean error statistics for last season are also included for the purposes of a comparison. Forecast tracks are only verified when a depression reaches tropical storm status.

2. Tropical cyclone activity

Tropical cyclone activity
 NWPNEPNATNITOTAL
Tropical depressions (<34 knots)5(4)5(3)2(2)0(0)12(9)
Tropical storms (>34 knots, <64 knots)6(10)5(12)7(6)1(4)19(32)
Hurricanes/typhoons (>64 knots)8(14)3(8)12(3)4(1)23(26)
Total19(28)13(23)21(11)5(5)58(67)

Categories assigned based on 1-minute averaged winds

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)

The number in brackets indicates the figure for the 2009 season.

3. Summary of all northern hemisphere storms

3.1 North-west Pacific basin storms

Mean Error Statistics
 T+0T+24T+48T+72T+96T+120T+144
Possibly verified1291017452331710
Detection rate (%)1001001001009494100
Mean AT-5-44-84-156-102-164-279
Mean CT-185-12-19-145-357
Mean skill (%)*****375356***************
2009 skill (%)*****375255***************
Mean DPE34115200311363417515
* 2009 DPE 41114205309476664862
Intensity skill (%)*****453527425020

* DPE for all north-west Pacific storms in 2009 season

Plot of the observed tracks of all storms in the north-west Pacific basin
Forecast positional errors in the north-west Pacific basin
Forecast skill in the north-west Pacific basin

2010 was one of the most inactive seasons in this region on record. The La Niña event prevented storms from developing in the eastern parts of the region. Track forecast errors were very similar to those seen in the last few years at short lead times, but were lower at longer lead times. Skill against CLIPER was similar to last season. There was a slow bias in forecasts overall. The intensity tendency skill was 34% overall.

3.2 North-east Pacific basin storms

Table of mean error statistics
 T+0T+24T+48T+72T+96T+120T+144
Possibly verified5742322216106
Detection rate (%)100100100100815033
Mean AT-468-24-49-333-296
Mean CT-1492328190196
Mean skill (%)*****274357***************
2009 skill (%)*****153445***************
Mean DPE2381126147231396375
* 2009 DPE 4311322837363410181763
Intensity skill (%)*****29442754-20100

* DPE for all north-east Pacific storms in 2009 season

Plot of the observed tracks of all storms in the north-east Pacific basin
Forecast positional errors in the north-east Pacific basin
Forecast skill in the north-east Pacific basin

The 2010 season in this basin was the least active since 1977. Track forecast errors were the lowest ever recorded at all lead times. Skill scores against CLIPER were at their highest since 2002. There was a slight slow and right-of-track bias in forecasts at longer lead times. The intensity tendency skill was 38% overall.

3.3 North Atlantic basin storms

Table of mean error statistics
 T+0T+24T+48T+72T+96T+120T+144
Possibly verified18314511488654938
Detection rate (%)100979695949697
Mean AT-8-31-46-76-83-148-187
Mean CT1-4-19-251662
Mean skill (%)*****465861***************
2009 skill (%)*****455860***************
Mean DPE33112183249284349478
* 2009 DPE 451051802824146211135
Intensity skill (%)*****503617251919

* DPE for all North Atlantic storms in 2009 season

Plot of the observed tracks of all storms in the North Atlantic basin
Forecast positional errors in the North Atlantic basin
Forecast skill in the North Atlantic basin

2010 saw one of the most active Atlantic seasons on record. Track forecast errors were near to last season's values at short lead times, but much lower at longer lead times. Skill scores against CLIPER were similar to last season's high values. There was a slow bias in forecast tracks. The intensity tendency skill score was 33% overall.

3.4 North Indian Basin Storms

Table of mean error statistics
 T+0T+24T+48T+72T+96T+120T+144
Possibly verified3626168310
Detection rate (%)10010094100100100*****
Mean AT-6-75-15258367768*****
Mean CT5-599339199-537*****
Mean skill (%)*****194664***************
2009 skill (%)*****-34***********************
Mean DPE52134253480525938*****
* 2009 DPE 79220521****************
Intensity skill (%)*****46337533100*****

* DPE for all North Indian storms in 2009 season

Plot of the observed tracks of all storms in the North Indian basin
Forecast positional errors in the North Indian basin
Forecast skill in the North Indian basin

Cyclone activity was average in 2010 in terms of number of storms, but most of these reached a high intensity and persisted for several days. Track forecast errors were near the long term average at short lead times, but higher than the average at long lead times. The intensity tendency skill was 37% overall.

3.5 Combined statistics for whole northern hemisphere

Table of mean error statistics
 T+0T+24T+48T+72T+96T+120T+144
Possibly verified4053142361701177754
Detection rate (%)100989898929091
Mean AT-6-34-58-88-72-152-210
Mean CT01034-23-18
Mean skill (%)*****405559***************
2009 skill (%)*****334954***************
Mean DPE34111185266307377482
* 2009 DPE44116210320498707918
Intensity skill (%)*****453724332522

* DPE for all northern hemisphere storms in 2009 season

Forecast positional errors for the whole northern hemisphere
Forecast skill for the whole northern hemisphere
Along-track errors for the whole northern hemisphere
Cross-track errors for the whole northern hemisphere
Intensity skill for the whole northern hemisphere.

Overall, activity in the northern hemisphere in 2010 was the lowest in recent history despite the active Atlantic season. Track forecast errors were either the lowest or second lowest ever achieved. Errors were particularly low relative to past years at longer lead times. Skill scores against CLIPER were the highest ever achieved. Last season's left-of-track bias was eradicated and the slow bias reduced. Detection percentages were fairly high, although a small proportion of storms were not detected as early as 24 hours into the forecast. The intensity tendency skill was 34% overall, which is slightly lower than the last couple of years.

Further tropical cyclone information

The Met Office web pages contain information on tropical cyclone forecasting at the Met Office. Monthly updates of tropical cyclone activity and forecasts are made, together with observed and forecast track information of recent storms, track prediction error statistics, lists of names and real time tropical cyclone forecast guidance.

Tropical Cyclone information can be found on the home page under the "Weather/World" heading.

Seasonal summaries of tropical cyclone activity and forecasts have been issued since the 1994-5 Southern Hemisphere season. To obtain these or any further information on tropical cyclone forecasting email the Met Office.

________________________

Acknowledgements

Mr.S.Lord, NMC, Washington, USA and Mr.C.Mauck, FNOC, Monterey, USA supplied CLIPER models for various basins.
Mr.S.Lord and Dr.M.Fiorino supplied GrADS software used to produce track plotting charts.

Last updated: 17 December 2013