Is the 2011 Hurricane Season Forecast a Bust?

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Accosted is the wrong word, but on two occasions this past weekend “friends” of mind said something along these lines: “Hey, Weatherman! Where are all the hurricanes you and your ilk predicted.” I told them to go back to cutting the grass, but their curiosity isn’t unfounded.

The climatological peak of hurricane season is at/near September 10. Still, the first three weeks of October are about on par with mid-August. In other words, the next two or three weeks of the season can still be quite active. Image: ImpactWeather

As of today, with Tropical Storm Ophelia racing off to the northeast past Newfoundland and Tropical Storm Phillippe hinting at intensification beyond 24 hours, there have been 16 named storms but only four hurricanes. To put this in perspective, a normal season – based on climatology – would see a season total of 9-12 named storms, with 5-7 hurricanes and 1-3 major hurricanes (category 3 or higher). Preseason forecasts indicated the 2011 season would be more active than normal, but not by much. As an example, Colorado State’s Philip Klotzbach (the keynote speaker at the 2010 and 2011 ImpactWeather Hurricane Seminar) preseason forecast indicated 16/9/5 (named/hurricanes/majors), NOAA’s broad forecast was 14-19/7-10/3-5, while ImpactWeather’s forecast of 14/8/4 was just a little bit lower than the Klotzbach prediction.

With the closing of the Cape Verde season (eastern Atlantic), focus now shifts west to the western Atalntic and Caribbean Sea for prime development areas. Red dots represent previous storm formation points, yellow arrows represent typical movement of storms and red highlighted areas indicate prime development regions. Image: ImpactWeather

Where are all the hurricanes? Indeed that is the question. The answer however, remains unclear. Yes, the Saharan air layer (SAL) can be blamed for part of the inactivity, but not all of it. Forecasters and computer models take the SAL into consideration with each forecast, but for a forecast to be so far off it’s usually something unexpected that is to blame. For instance, mid-latitude dry air is thought to be having an affect on the lower number of hurricanes this year. For much of the summer Europe had a strong high pressure system in place and that dry air, driven clockwise off the southern edge of the high, intruded into the Atlantic. Dry air is not conducive to hurricane formation. Further post-season analysis will be required no doubt, but there is still a third of the hurricane season to come. The final nail has yet to be driven into the coffin known as the 2011 Atlantic Hurricane Season.

Far from it.

By mid-month, the focus continues its westward trend. Image: ImpactWeather

In fact, as if being delivered by FedEx just as the focal point of tropical storm generation shifts to the Caribbean, the MJO is about to arrive in the eastern Pacific — and the Madden-Julian Oscillation is well-known as a hurricane season enhancer. Consider the MJO as a “pulse,” or an atmospheric wave that travels eastward from the Indian Ocean with enhanced thunderstorm and tropical activity associated with it. With the MJO moving into such a position, it is expected to produce a potential flare of tropical activity in the Caribbean and Gulf of Mexico over the next few weeks.

But is it enough to bring the number of Atlantic storms in line with preseason forecasts? Only time will tell, but to expect an additional four storms to reach the ImpactWeather preseason forecast, or the five storms predicted by the Klotzbach forecast? That may be asking too much. The climatological peak of hurricane season is September 10. After the tenth, we start to see fewer storms as the tropical North Atlantic begins to see the early signs of the approaching winter. By this time, we also see the end (or the beginning of the end) of the Cape Verde season, leaving the most prime development regions to be the Caribbean, the southwestern waters of the North Atlantic and the Gulf of Mexico. Timed with the arrival of the MJO as mentioned previously, it may be too early indeed to lay to rest the current Atlantic storm season, but time is short if the preseason forecast is to be a success.

And let’s not forget that late season storms can still be quite catastrophic. The “W” storm in 2005, Wilma, formed on October 15th east southeast of Grand Cayman in the Caribbean Sea, then moved generally west to the Yucatan Peninsula then curved sharply northeast to make landfall as a major hurricane on the southwestern coast of Florida on October 24. All told, Hurricane Wilma was directly responsible for 23 deaths and more than $23 billion dollars in damage, which ranks the storm in the top five of costliest storms ever recorded in the North Atlantic.

Category 4 Hurricane Wilma near the Yucatan Peninsula. Image: NOAA

















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