Consequences, Intended and Unintended, of Tropical Cyclone Surveillance Globally during 2008

During summer and autumn 2008, concurrent extensive surveillance of tropical cyclones in both the Atlantic and Western Pacific basins were conducted for the first time as part of the NOAA Hurricane Field Program and the THORPEX-Pacific Area Regional Campaign. From 27 August through 01 October, eighteen tropical cyclones were active globally according to reports from the National Hurricane Center and the Joint Typhoon Warning Center . The large number of cases in all basins allows for an assessment of the impact of the dropwindsonde data from on global tropical cyclone forecasts in the NOAA Global Forecasting System. The dropwindsonde data from both field programs improved average track forecasts at all forecast times by up to 13%, and the improvements were statistically significant at the 90% level with serial correlation removed at all forecast times through 84 h. These included six in the Atlantic, three in the Eastern Pacific, one in the northern Indian Ocean, and eight in the Northwestern Pacific basins. Three of the six in the Atlantic and four in the Northwestern Pacific basins were sampled with aircraft.

Improvements in the Western Pacific ranged from 4 – 23%, and those in the Atlantic from -3 to 12%. Because of the small numbers of cases in the East Pacific and Indian basins, the average impacts were large. The impacts in the Atlantic correspond to previously published results in that the impact decreases in time and becomes negligible by 84 h. This contrasts with results from the West Pacific in which impacts remain about steady through 120 h. Analysis of individual cases shows that the dropwindsonde data obtained around some tropical cyclones has about as much impact on track forecasts on other tropical cyclones within the basin or around the world as on the targeted tropical cyclone itself.