Tropical cyclone verification northern hemisphere 2018

1. Introduction

A summary of tropical cyclone activity in the Northern Hemisphere for the 2018 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

Categories assigned based on 1-minute averaged winds

The number in brackets indicates the figure for the 2017 season.

3. Summary of all northern hemisphere storms

3.1 North-west Pacific basin storms

* DPE and skill for all north-west Pacific storms in 2017 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

2018 saw slightly more activity than 2017, particularly for typhoons. Track forecast errors were close to last season's values at all but the longest lead times. Skill against CLIPER was again at high levels. A strong bias (as measured by central pressure) was present from 72 hours onwards.

3.2 North-east Pacific basin storms

* DPE and skill for all north-east Pacific storms in 2017 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 exceptionally high activity is this basin in 2018. Track forecast errors were lower than last season. Skill scores against CLIPER were higher than last season. The intensity bias (as measured by central pressure) was slightly positive indicating a weak bias.

3.3 North Atlantic basin storms

* DPE and skill for all North Atlantic storms in 2017 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

2018 saw similar activity to 2017, although less hurricanes. Track forecast errors were a little higher than last season. Skill scores against CLIPER were a little below last season's values. A large strong bias (as measured by central pressure) was apparent at longer lead times.

3.4 North Indian Basin Storms

* DPE and skill for all North Indian storms in 2017 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 much higher than in recent seasons. Track forecast errors were a little above values from recent seasons. There was a slight strong bias in forecasts (as measured by central pressure).

3.5 Combined statistics for whole northern hemisphere

* DPE and skill for all northern hemisphere storms in 2017 season

There was greater tropical cyclone activity in 2018 than 2017, particularly in the North-East Pacific and North Indian basins.

Track forecast errors were at similar values to that seen in the previous four seasons. Skill scores against CLIPER were similar to the last two seasons' values. Cross track errors were generally small this season. There was a slight slow bias in forecasts, but less so than last season.  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

There was a continued downwards trend in the five-year running mean of track forecast errors.

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. However, the bias was not as large as in 2017. 10m winds had a weak bias which reduced with lead time, but was still apparent at long lead times.

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.