An assessment of NOGAPS performance in the prediction of tropical Atlantic circulation formation
Dorics, Theodore G.
Elsberry, Russell L.
Harr, Patrick A.
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The Navy requirement for 5-day tropical cyclone track guidance necessitates an assessment of the Navy Operational Global Atmospheric Prediction System (NOGAPS) in forecasting tropical cyclone formation. The Tropical Cyclone Vorticity Tracking Program is applied to NOGAPS analyses and forecasts through 120 h to identify and track circulations in the tropical Atlantic region from 25 July - 31 October 2001. Circulations over northern South America were not found to be related to Atlantic hurricane formation and the number of formations in the western Atlantic was insufficient for statistical analysis. Circulation formations over Africa tend to be forecast too early while those forming over the eastern Atlantic tend to be forecast late. About 70% of the NOGAPS forecasts and analyzed formations are within +/- 12 h regardless of forecast intervals, and about 12% of the formation forecasts are false alarms. Whereas the on-time formations tend to have small relative vorticity errors, the early (late) formation forecasts are at first too strong (weak), but then the model error growth dominates the expected timing error contribution. At the time the National Hurricane Center issues a tropical storm warning, the NOGAPS forecasts of relative vorticity, sea-level pressure, and circulation size generally have smaller amplitudes than the verifying analyzed values.
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