Tropical Weather Discussion - 2009

By Rob Lightbown, Crown Weather Services

Issued: Tuesday, April 7, 2009 720 pm EST

Discussion

This is an update to my previous look at the possibilities for the 2009 Hurricane Season. As many of you know, Colorado State University and Tropical Storm Risk, Inc have released their April forecast updates for the 2009 Hurricane Season. I have taken a look at both forecasts and have cross-referenced the material in the forecasts. What I have found is pretty interesting and I am going to go over this with you.

The first item of interest is that Colorado State is forecasting 12 Named Storms, 6 of those Storms becoming Hurricanes and 2 of those Hurricanes becoming Major Hurricanes. The current La Nina conditions are expected to transition into at least neutral conditions and very possibly El Nino conditions by the later parts of the Hurricane Season. If El Nino conditions do develop, it would increase levels of vertical wind shear and thus decrease levels of Atlantic hurricane activity.

Another factor to watch is the anomalous cooling of sea surface temperatures in the tropical Atlantic. Cooler waters are associated with less Atlantic hurricane activity. There is some question on whether this cooling will continue. The Azores High has been somewhat weaker than average during March 2009, implying weaker trade winds which should lead to some anomalous warming in the Main Development Region. If this occurs then hurricane activity may be more active than what is being forecast.

There are five hurricane seasons that have characteristics most similar to what was observed during February and March of 2009. These seasons are 1951, 1968, 1976, 1985 and 2001. One very interesting aspect regarding four out of the five years is that there was significant tropical storm development in May and June. In fact, 1951 had a major hurricane in mid to late May off of the US southeast coast. So, I am going to go out on a limb and forecast that there will be tropical storm or hurricane development close to the US coast between May 15 and June 5.

I still think we need to really watch the US East Coast, eastern Gulf of Mexico and Florida this hurricane season. Of the analog years: 1951, 1968, 1976 and 1985 had significant activity in these areas. Two things to note: (1) 1976 and 1985 had New England strikes (Belle as a tropical storm in 1976 and Gloria as a hurricane in 1985). (2) 1968 and 1985 had hurricane strikes on the eastern Gulf of Mexico (Category 1 Gladys in 1968 north of Tampa and Elena in 1985 which loop de looped around the eastern Gulf of Mexico and finally landfalled near Biloxi Mississippi as a Category 3 hurricane).

Another item I noticed is that there was early season activity along the Texas coast during 1968 and 2001, so it is not impossible for activity early in the season (May or June) along the Texas coast and it will be something to watch for.

As for the Caribbean Islands: 1951 and 2001 had major hurricanes that were Caribbean cruisers while 1968 and 1985 had storms forming in the western Caribbean. So, those of you in the Caribbean Islands shouldn’t let your guard down as I think there is a pretty good chance for a tropical storm or hurricane affecting the Caribbean this year.

Now onto Tropical Storm Risk’s 2009 Hurricane Season Forecast: They are calling for an active hurricane season: 15 named storms, about 8 of those storms becoming hurricanes and about 3 to 4 of those hurricanes becoming major hurricanes. The major reason why TSR’s numbers are higher is because of slower than normal trade winds from July to September over the Main Development Region for hurricanes over the Atlantic. Trade winds are forecast to be about 1 mph slower than average in this region, which could allow for more storms to form and also allow the oceans to heat up due to reduced evaporational cooling.

So, to sum it up: I do think we will have very early season development and believe that there will be a tropical storm or hurricane forming close to the US coast between May 15 and June 5.

The main areas to watch this season are the US East Coast, Florida and the eastern Gulf of Mexico with a lesser threat along the Texas coast early in the hurricane season.

Finally, all areas of the US coastline and Caribbean islands are at risk every hurricane season and you should not become complacent. All it takes is one hurricane to ruin your day!!! So, all residents and vacationers along the coast should stay abreast of tropical storm and hurricane advisories throughout the 2009 Hurricane Season. Prepare now for the 2009 Hurricane Season. To help you prepare, visit these sites for more information:

OneStorm Hurricane Preparedness
National Hurricane Center's Preparedness Page
American Family Safety

I will begin issuing daily tropical weather discussions on Monday, June 1st unless there is tropical cyclone activity during May. If that happens, then I would issue tropical weather discussions to cover that.