Weather Research Center TM

WRC’s OCSI® Model Tropical Cyclone Predictions seems closer this year than others forecasts

HOUSTON – Weather Research Center [WRC]’s Orbital Cyclone Strike Index [OCSI®]predicted that this would be a very inactive tropical system and there would be only six named tropical storms in the Atlantic. This year there have been 3 named storms so far and the tropics are remaining fairly quiet.

Meteorologists Jill F. Hasling and Dr. John C. Freeman of Weather Research Center never adjust their hurricane forecast. In November of 2001, Jill Hasling gave the Center’s prediction of 6 named storms, with 3 becoming hurricanes. Once the forecast is issued in January or February the forecast does not change. Unlike their colleagues, their original forecast called for a below average year. Weather Research Center’s main forecast indicates which coast of the US has the highest risk of experiencing a tropical storm. This year that is the West Coast of Florida, which has an 80% chance of experiencing a tropical storm or hurricane. The second highest risk coasts are the Texas coast and Louisiana to Alabama coast, each with a 60% chance. The Gulf of Mexico oil leases have an 81% chance of experiencing a tropical storm this year. The Gulf of Mexico forecast and the Louisiana forecast has verified this year with Tropical Storm Bertha making landfall along the Louisiana Coast.

A secondary prediction from the Orbital Cyclone Strike Index [OCSI] model is the prediction of the number of named storms expected in the Atlantic and Gulf of Mexico. The outlook, released in November 2001, called for a below normal season for the number of storms. The prediction is for 6 named systems with 3 of these storms intensifying into hurricanes. On average there are 9.7 named tropical storms per year with 5.7 of the storms intensifying into hurricanes.

Jill Hasling stated in November that " In the past eleven years where the phase of the OSCI was the same as this year, eight of the years had six or less named storms. Six of the eleven years were El Niño Years. This statement has verified with the El Niño establishing itself this summer. Dr. John Freeman’s long range forecast, released in 1998, called for a 40% chance of an ENSO event year in 2002, so there is a good chance that this will be an El Niño year.

When you compare WRC’s OCSI forecast of the number of tropical cyclones with Dr. William Gray’s earliest prediction each year of the number of tropical cyclones with the number cyclones observed you find that WRC has come within 2 storms more or less ten times and Dr. Gray has come within 2 storms more or less five times. Dr. Gray adjust his forecast up and down several times during the season. WRC never changes their forecasts of the number of storms. See the table and graphs below:

Positive number indicates the number of years over-forecast each year. Negative numbers indicate the number of storms under forecast. If you use ±2 then WRC was the closest 7 out of the 17 years with 3 years in a tie which makes a total of 10 year. Dr. William Gray was closest 2 years out of the 17 years with three ties making a total of 5 years. This is based on Dr. Gray’s in April since 1995 and his earliest forecasts for years prior to 1995.

The Orbital Cyclone Strike Index [OCSI] model, developed at Weather Research Center by Dr. Freeman and Ms. Hasling, is based on the premise that there are orbital forces that influence the global circulation pattern on the sun and subsequently, the global circulation pattern of the earth. The sun's circulation pattern is tracked by the sun spot cycle. Using this solar cycle to make an index, hurricane climatology has been summarized into an index called the OCSI. This index has been used since 1985 to make annual forecasts of the section of North American coast that has the highest risk of experiencing a tropical storm or hurricane. Meteorologists at the Center can make their hurricane outlook for the next ten years when the year of the sunspot minimum is determined.

The hurricane season is far from over. The season lasts until November 30 and everyone is urged to keep an eye on the tropics even though the number of storms is forecast to be below normal.

In addition to its ongoing research, the Center also provides storm and hurricane information via the Internet through Storm Navigator. This service helps people navigate weather information on the Internet as well as providing detailed storm updates and related information. All of the Center's projections including past predictions can be found on the Internet, http://www.wxresearch.com/outlook.

Jill F. Hasling and Dr. John C. Freeman are both Certified Consulting Meteorologist and Fellows of the American Meteorological Society. Both are researchers and founding directors of the Weather Research Center, which is a non-profit educational and research facility, based in Houston, Texas. Dr. Freeman has over 50 years of meteorological experience and Ms. Hasling has over 28 years experience. Both have been involved in tropical meteorology research and have been working together on this forecast method since 1985.