Major Hurricane Felix roared ashore at Category 5 strength along the northeast coast of Nicaragua close to the Honduras border. Felix strengthened during the predawn hours as it went through an Eyewall Replacement Cycle. During this cycle, the sustained wind initially dropped late yesterday, but then rapidly strengthened during the completion of the cycle just before landfall. This marks the second category 5 landfall this season. Both Dean and Felix fed off nearly perfect surface and upper level conditions to pull off such feats. There is a lot of talk about the warm water being the main ingredient. Well, it is one important ingredient, but not the only one. The Caribbean waters are always going to be warm, it is a low latitude body of water. So, yes, during the height of the hurricane season, you can bet on the warmest water of the season. Upper atmospheric conditions play a huge part in a storms survival. During both Dean and Felix, a strong ridge of high pressure was situated north of the storm. The same ridge of high pressure that brought our region the extreme heat. The strength of that "high" allowed Dean first of all to be well ventilated and lacking of any shear to disrupt its development. A slightly weaker, but otherwise strong ridge again is positioned over the US southeast and Gulf which steered Felix and created similar perfect conditions for development. The developing La Nina conditions off the western South America coast plays a role in these upper level conditions. La Nina is the opposite of El Nino. It is a cooling of the waters off the South American coast which also affects global weather patterns and occurs on intervals opposite of El Nino. When a La Nina is developing or is in place, we expect hurricane conditions to be above normal. This occurs because La Nina creates a lack of wind shear in the tropical development region. With a lack of shear, storms can more easily develop and strengthen. During an El Nino episode, wind shear increase in the tropical development region and that can serve to prevent development or help weaken a developed storm. So, year in and year out, the Caribbean waters are plenty warm, but it's the upper level factors that go a long way in determining the outcome of a storm.
Another area to watch for development is off the southeast US coast. Currently, it is a non tropical low. But, should it continue drifting off the coast around the region of the warm, Gulf Stream waters, the "low" could become a warm core, or tropical system. Some computer model guidance shows this system drifting for 24-48 hours before gaining some strength and backing west toward the coast. So, as we enter the peak of the hurricane season there is a lot to watch.
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