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Average hurricane season foreseen by TSR

By: Dr. Jeff Masters, 1:33 PM GMT on June 04, 2009

The ballots are all in now, and all three major seasonal forecasting groups are calling for a near-average Atlantic hurricane season in 2009--the British private forecasting firm Tropical Storm Risk, Inc. (TSR) has joined the ranks of NOAA and Colorado State University in calling for near-average activity. The latest TSR forecast issued today calls for 10.9 named storms, 5.2 hurricanes, 2.2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 72% of average. The storm numbers are close to the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes, and are sharp reduction from their April forecast of 15 named storms, 7.8 hurricanes, and 3.6 intense hurricanes. TSR predicts a 50% chance that this season will be in the bottom 1/3 of years historically, and a 40% chance that U.S. landfalling activity will be in the lowest 1/3 of years historically. TSR gives a 32% chance of a near-normal season, and a 17% chance of a below normal season. TSR rates their skill level as 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.2 named storms will hit the U.S., with 1.3 of these being hurricanes. The averages from the 1950-2008 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these April forecasts for U.S. landfalls is 7 - 18% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 0.9 named storms, 0.4 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their reduced forecast: a large and unexpected cooling of sea surface temperatures in the tropical Atlantic, and warmer SSTs in the Equatorial Eastern Pacific (which might lead to an El Niño event that will bring high wind shear to the Atlantic). TSR expects faster than than normal trade winds from July - September over the Main Development Region (MDR) for hurricanes over the Atlantic (the region between 10° - 20° N from Central America to Africa, including all of the Caribbean). Trade winds are forecast to be 0.83 meters per second (about 1.7 mph) faster than average in this region, which would create less spin for developing storms, and allow the oceans to cool down, due to increased mixing of cold water from the depths and enhanced evaporational cooling. TSR forecasts that SSTs will cool an additional 0.3°C compared to average over the MDR during hurricane season.

Portlight.org offering relief to Florida flood victims
Tropical disturbance 90L dropped as much as two feet of rain over Northeastern Florida in May, causing severe flooding. In Volusia County, at least 1500 homes were damaged by the flooding, and many of these were in low-income housing projects where the residents did not have flood insurance. Portlight Strategies, Inc., is now working to assist in this area by providing durable medical equipment to the disabled, elderly, or injured that have lost equipment due to the flooding. Specifically, the Portlight team will be assisting with the rebuilding of two homes. One of the homes is owned by a single mother who stood in her house crying, in two feet of water, as she prepared to go to her daughters graduation. The other home is owned by a elderly woman whose husband passed away two years ago. Neither of these families had flood insurance, and can not afford even the lowest interest rate loans provided by FEMA. Portlight's work in Holly Hill, FL will begin on Friday June 12; if you are interested in volunteering, please contact John Wilbanks, john@portlight.org 843-200-6022. There are plenty of stories very similar to these two. Portlight's ability to help is only limited by your assistance, so please consider volunteering or donating today by visiting the Portlight disaster relief blog..

Figure 1. Rainfall amounts over Florida for the two weeks ending on May 27, 2009. Image credit: NOAA.


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.