The 23rd Conference on Hurricanes and Tropical Meteorology

P7A.14
VERIFICATION OF THE PREDICTION OF THE RISK OF TROPICAL STORM AND HURRICANE STRIKES ALONG THE NORTH ATLANTIC COAST FOR THE PERIOD 1985-1997

John C. Freeman, Weather Research Center, Houston, TX; and J. F. Hasling

Abstract: A forecast tool has been developed called the Orbital Cyclone Strike Index [OCSI] to make the risk assessment of a tropical cyclone strike along the North American coast each year. The OCSI is based on the premise that the sun’s orbit causes changes in the torque on the earth's atmosphere that are similar to the changes in the torque of the sun’s atmosphere which can be traced through the solar cycle. The authors use this premise to create the index based on the solar cycles. The OCSI has been used for forecasting tropical storms and hurricane landfalls since 1985. This paper compares these forecasts to the actual events. Two types of forecasts were verified, the first one was the prediction of the likelihood of a hurricane or tropical storm making landfall on a certain section of the Atlantic coast of North America. This forecasts included predictions of when tropical cyclone strikes were likely as well as a forecasts when tropical cyclones were unlikely. This was a forecast that was designed to test the theory. The phases of the OSCI and the coast that were chosen to forecast a strike were selected were selected as outlined below. The phases and coasts chosen for a strike had an expectation that was equal to or more than the mean expectation for the coast plus one standard deviation of the expectation for a phase. The phases and coasts chosen for no strike had an expectation that was equal or less than the mean expectation minus one standard deviation. This rule allowed us to make 12 forecasts of strikes and 7 forecasts of no strikes per cycle. The OCSI was tested as a forecast tool over 10 cycles and found accuracy from 57% to 100% with most of them near 70%. The second forecast was to predict which section of the coast line each year had the highest and second highest probability of experiencing a tropical cyclone. The first type of forecasts was verified from 1987 to 1996. The second type of forecasts was verified for the coasts and the phases of the solar cycle that had the highest probability each year and those that had the second highest probability each year and was verified for the years 1985 to 1987. The first type of forecast for strikes verified 67% and the expectation in this case was 71%. The authors considered this a good forecast. The verification for no strikes verified 75% and the expectation for no strike was 78%.

The 23rd Conference on Hurricanes and Tropical Meteorology