Tropical cyclone verification northern hemisphere 2019
A summary of tropical cyclone activity in the Northern Hemisphere for the 2019 season together with an assessment of the performance of the Met Office global model in predicting the track and intensity of these tropical cyclones.
1. Introduction
A summary of tropical cyclone activity in the Northern Hemisphere for the 2019 season is presented below together with an assessment of the performance of the Met Office global model in predicting the track and intensity 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+168, although statistics are only presented at 24-hour intervals in this report. The global model resolution in operation was 0.140625° x 0.09375° x 70 levels. This is equivalent to a horizontal resolution of 16 km × 10 km at the equator.
Tropical cyclone forecast verification - measures of error
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
| NWP | NEP | NAT | NI | TOTAL | |
| Tropical depressions (<34 knots) | 4 (7) | 2 (3) | 2 (1) | 0 (0) | 8 (11) |
| Tropical storms (34-63 knots) | 12 (12) | 12 (10) | 12 (7) | 2 (4) | 38 (33) |
| Hurricanes/typhoons (>63 knots) | 16 (16) | 7 (13) | 6 (8) | 6 (4) | 35 (41) |
| Total | 33 (35) | 21 (26) | 20 (16) | 8 (8) | 81 (85) |
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 2018 season.
3. Summary of all northern hemisphere storms
3.1 North-west Pacific basin storms
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | T+144 | T+168 | |
| Possibly verified | 266 | 208 | 161 | 120 | 83 | 52 | 29 | 17 |
| Detection rate (%) | 100 | 99 | 99 | 99 | 100 | 98 | 97 | 100 |
| AT error (km) | 2 | -14 | -39 | -57 | -66 | -38 | -177 | -179 |
| CT error (km) | 1 | -15 | -19 | -28 | -40 | -27 | 105 | 225 |
| Track skill (%) | ***** | 57 | 63 | 66 | ***** | ***** | ***** | ***** |
| * 2018 skill (%) | ***** | 65 | 74 | 76 | ***** | ***** | ***** | ***** |
| DPE (km) | 39 | 79 | 143 | 204 | 274 | 344 | 447 | 663 |
| * 2018 DPE (km) | 33 | 68 | 110 | 171 | 249 | 370 | 588 | 811 |
| Central pressure bias (mb) | 4.9 | 5.9 | 5.3 | 1.0 | -6.3 | -11.3 | -13.3 | -16.9 |
* DPE and skill for all north-west Pacific storms in 2018 season
Plot of the observed tracks of all storms in the north-west Pacific basin
Track forecast errors in the north-west Pacific basin
Track forecast skill in the north-west Pacific basin
2019 saw slightly activity close to that seen in 2018. At short lead times, track forecast errors were higher and skill scores lower than 2018. However, track forecast errors at longer lead times were lower. There was a strong bias (as measured by central pressure) in forecasts at longer lead times.
3.2 North-east Pacific basin storms
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | T+144 | T+168 | |
| Possibly verified | 134 | 98 | 75 | 57 | 41 | 28 | 18 | 10 |
| Detection rate (%) | 100 | 95 | 93 | 93 | 98 | 100 | 94 | 80 |
| AT error (km) | 7 | 11 | 20 | 46 | 55 | 93 | 195 | 40 |
| CT error (km) | -7 | 11 | 20 | 46 | 55 | 93 | 195 | 40 |
| Track skill (%) | ***** | 49 | 67 | 66 | ***** | ***** | ***** | ***** |
| * 2018 skill (%) | ***** | 58 | 71 | 75 | ***** | ***** | ***** | ***** |
| DPE (km) | 35 | 78 | 110 | 151 | 196 | 274 | 377 | 405 |
| * 2018 DPE (km) | 39 | 70 | 116 | 173 | 241 | 325 | 380 | 419 |
| Central pressure bias (mb) | 2.9 | 3.7 | 3.8 | 1.6 | -0.8 | -1.2 | 0.1 | -1.9 |
* DPE and skill for all north-east Pacific storms in 2018 season
Plot of the observed tracks of all storms in the north-east Pacific basin
Track forecast errors in the north-east Pacific basin
Track forecast skill in the north-east Pacific basin
There was slightly less activity this year than in 2018 due to less hurricanes. Track forecast errors were either close to or lower than last season. Skill scores against CLIPER were a little down on last season. The intensity bias (as measured by central pressure) was fairly neutral.
3.3 North Atlantic basin storms
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | T+144 | T+168 | |
| Possibly verified | 141 | 108 | 89 | 69 | 55 | 40 | 28 | 20 |
| Detection rate (%) | 100 | 99 | 99 | 97 | 100 | 98 | 100 | 100 |
| AT error (km) | -2 | -25 | -45 | -13 | 69 | 14 | 52 | 42 |
| CT error (km) | -1 | -9 | -2 | 17 | 20 | -13 | -34 | -126 |
| Track skill (%) | ***** | 66 | 67 | 68 | ***** | ***** | ***** | ***** |
| * 2018 skill (%) | ***** | 69 | 74 | 73 | ***** | ***** | ***** | ***** |
| DPE (km) | 27 | 70 | 148 | 227 | 301 | 281 | 360 | 487 |
| * 2018 DPE (km) | 30 | 63 | 126 | 216 | 303 | 378 | 490 | 556 |
| Central pressure bias (mb) | 5.1 | 3.4 | 0.7 | -3.3 | -6.1 | -3.0 | -0.9 | 4.5 |
* DPE and skill for all North Atlantic storms in 2018 season
Plot of the observed tracks of all storms in the North Atlantic basin
Track forecast errors in the North Atlantic basin
Track forecast skill in the North Atlantic basin
The number of storms was high in 2019, but many of these were short lived. Track forecast errors were higher than last season at short lead times, but lower at longer lead times. The intensity bias (as measured by central pressure) was relatively small.
3.4 North Indian Basin Storms
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | T+144 | T+168 | |
| Possibly verified | 83 | 67 | 52 | 39 | 27 | 18 | 10 | 2 |
| Detection rate (%) | 100 | 99 | 10 | 100 | 100 | 94 | 80 | 100 |
| AT error (km) | -3 | 0 | -28 | -50 | -141 | -306 | -475 | -508 |
| CT error (km) | -1 | -13 | -28 | -34 | -32 | -30 | -99 | -99 |
| Track skill (%) | ***** | 57 | 52 | 63 | ***** | ***** | ***** | ***** |
| * 2018 skill (%) | ***** | 33 | 65 | 70 | ***** | ***** | ***** | ***** |
| DPE (km) | 37 | 75 | 147 | 177 | 254 | 375 | 531 | 585 |
| * 2018 DPE (km) | 55 | 103 | 147 | 200 | 222 | 333 | 452 | 784 |
| Central pressure bias (mb) | 0.7 | -0.6 | -1.4 | -3.6 | -7.9 | -10.2 | -23.5 | -22.0 |
* DPE and skill for all North Indian storms in 2018 season
Plot of the observed tracks of all storms in the North Indian basin
Track forecast errors in the North Indian basin
Track forecast skill in the North Indian basin
Cyclone activity was the highest seen for some decades with a particularly high number of hurricane strength tropical cyclones. Track forecast errors were mixed compared to last season. There was a strong bias in forecasts (as measured by central pressure) at longer lead times.
3.5 Combined statistics for whole northern hemisphere
| T+0 | T+24 | T+48 | T+72 | T+96 | T+120 | T+144 | T+168 | |
| Possibly verified | 624 | 481 | 377 | 285 | 206 | 138 | 85 | 49 |
| Detection rate (%) | 100 | 98 | 98 | 98 | 100 | 98 | 95 | 96 |
| AT error (km) | 1 | -9 | -27 | -26 | -16 | -29 | -49 | -62 |
| CT error (km) | -1 | -16 | -23 | -23 | -23 | -3 | 29 | 15 |
| Track skill (%) | ***** | 58 | 64 | 66 | ***** | ***** | ***** | ***** |
| * 2018 skill (%) | ***** | 63 | 73 | 74 | ***** | ***** | ***** | ***** |
| DPE (km) | 35 | 76 | 139 | 196 | 263 | 315 | 411 | 541 |
| * 2018 DPE (km) | 36 | 70 | 118 | 185 | 259 | 354 | 470 | 557 |
| Central pressure bias (mb) | 4.0 | 4.0 | 3.0 | -0.6 | -5.4 | -6.7 | -7.2 | -5.5 |
* DPE and skill for all northern hemisphere storms in 2018 season
Levels of tropical cyclone activity were mostly near 2018, with the North Indian basin being particularly active compared to usual.
Track forecast errors were higher at shorter lead times, but lower at longer lead times compared to recent seasons. Skill scores against CLIPER were slightly down on recent seasons. Cross track errors were generally small this season. There was a slight slow bias in forecasts. Detection percentages were mostly high.
Track forecast errors for the whole northern hemisphere
Track forecast skill for the whole northern hemisphere
Cross-track errors for the whole northern hemisphere
Along-track errors for the whole northern hemisphere
The five-year running mean of track forecast errors is starting to flat line now that the large reduction seen in 2014 following the introduction of a new forecasting system has exited the figures.
Five-year running mean track forecast errors for the whole northern hemisphere
The intensity bias as measured by central pressure was small at short lead times and became negative (strong bias) at longer lead times. This was similar to 2018. 10m winds had a weak bias which reduced with lead time, but was still apparent at long lead times as in 2018.
Central pressure forecast bias for the whole northern hemisphere
Peak 10m wind forecast bias for the whole northern hemisphere
4. Further tropical cyclone information
The Met Office tropical cyclone 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 information of recent storms, track and intensity prediction error statistics, lists of names and real time tropical cyclone forecast guidance.
For further information on tropical cyclone forecasting email the Met Office.
