April 12, 2010

Getting Ready: An Early Preview of the 2010 Hurricane Season

Filed under: Tropical — Erin @ 10:28 am

From the point of view of a snow lover, it was an excellent winter. But that is now long over for those of us in the Eastern United States. Many areas have already hit 90°F! Here in MS we have not, but I anticipate that some spot in the Gulf Coast states will reach this wretched milestone early in May.

Before I get to the topic about a future event, I feel compelled to talk about one closer to the present. Severe weather season is upon us, though it is off to a slow start. The Southeastern states are arguably past the springtime peak and seem to have gotten off quite light, but we must not forget that it is the months of May and June when so many major tornado disasters have occurred. Jarrell, TX… Moore, OK… the May 2003 outbreak sequence… Greensburg, KS… Parkersburg, IA… those are all F5 or EF5 events except for 2003 (and even it had a tornado that was considered by some to have been underrated as F4). The list goes on, and it does not require an EF5 tornado to do massive, tragic damage. But it is very difficult to forecast severe weather more than a few days in advance, let alone a month or more.

Hurricane season is a different matter, and it is quite possible to make long-range forecasts about the overall activity level of a particular season, especially now that we are merely a month and a half away from the beginning of the Atlantic season. 2010’s hurricane season is not, I believe, going to be anything at all like 2009’s.

The strong El Nino event that gave the Eastern U.S. such a cold and snowy winter (and killed off much Atlantic hurricane activity) is fading fast. The majority of ENSO models predict a return to ENSO-neutral conditions by the June-July-August period (link: PDF).

However, El Nino has left its mark. As is typical following a significant El Nino event, sea surface temperatures in the eastern Atlantic are well above average, and in fact, the anomalies for this year are greater than the anomalies in April of 2005, a year that had record heat across the ocean. In the far eastern part of the ocean, there are areas that are already at 30°C.

Apr. 12, 2010:

Apr. 12, 2005:

Note: All graphics in this post are created by NOAA and are therefore public domain. I have downloaded the graphics current for 04/12/2010 to my server to avoid taking U.S. Government bandwidth. Links to the pages where these graphics were found will not point to the same images at dates in the future.

If this continues and shear decreases as expected, this year may be quite good for long-tracked Cape Verde systems. Indeed, these temperatures are apparently a record in terms of warmth.

The Gulf of Mexico is below average, but this is because of the cold winter. With surface temperatures reaching into the upper 70s and low 80s in the Gulf states for the foreseeable future, and little cloudiness to moderate the effect, it’s likely that this body of water will warm up. Indeed, observing the sea surface temperature anomaly maps for the past few weeks indicates that this warmup is occurring already.

A limiting factor at present may be wind shear, which is above the climatological average:


(Link takes you to the current shear map on NOAA.)

This will continue to be a limiting factor for cyclone development if it persists into the early season. However, as the El Nino fades, shear should decrease. Indeed, the current above-average level of wind shear may only be a temporary event, as overall it has been below average for much of the past several months:


(Link takes you to the current shear graph on NOAA.)

The Bermuda High, an area of high pressure that extends to the western Atlantic, is not yet established. The location of this feature will be important to watch, as it determines whether long-tracked Cape Verde hurricanes tend to strike land—and what landmasses that they strike—or recurve to sea. The farther west it goes, the more likely that such hurricanes will hit a coastline, but too far west and storms tend to be steered south of the United States, as was the case in 2007.

In short: Sea surface temperatures are likely not going to be a problem in 2010. I think the features to watch, here in the pre-season, will be the evolution of ENSO, the location of the Bermuda High, the warmup of the Gulf and far western Atlantic near the Bahamas, and the levels of wind shear as compared to climatology. If the ENSO level decreases to neutral by the peak of the season and shear decreases to the climatological average (and these two factors are very intimately connected, I should note), but sea surface temperatures continue to remain high, I fully expect to see some beasts brewed up and for “Category 5” to make a reappearance in this basin for the first time since 2007.

Unless the ENSO prediction models are mostly wrong, the Atlantic coasts are not going to get off light this year. It’s impossible yet to determine what areas are likely to be targeted, since we do not know how far west that the Bermuda High will set up, but at present I would go out on a limb and say that somebody is in for a bad year. It’s time to start getting ready.

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