Application of the Navy's numerical hurricane and typhoon forecast scheme to 1967 Atlantic tropical-storm data

Abstract

Renard recently reported on a numerical scheme for predicting the motion of tropical storms for intervals up to 72 hours. The forecast technique is applied in two steps. First, numerical geostrophic steering of the cyclone center is accomplished using Fleet Numerical Weather Central's analyses and prognoses of smoothed isobaric height fields, called Sr fields. Next, a statistical correction for vector bias in the numerical steering computation is used selectively in an attempt to improve the accuracy of the forecast track. The bias modification is dependent solely on the peculiarities of recent-history 12- and 24-hour forecasts in relation to the actual storm trajectory. Forecasts for intervals up to 72 hours, generated from the 1967 Atlantic operational storm positions, are compared to the results from previous experimental forecasts for 1965 using best-track positions of Atlantic storms. Results indicate the numerical scheme shows skill in relation to both 1965 and 1967 official-forecast accuracy as documented by Fleet Weather Facility, Jacksonville, Florida. In 1967, the relative improvement over official forecasts, using 700 mb prognostic SR fields for steering, ranges from 52% at forecast intervals of 7-18 hours to 9% at forecast intervals of 43-54 hours. Discussions of various forecast modes and selective modification schemes as well as stratification of error statistics by area, track, and storm stage are included. (Author)