Oct 27, 2011

DAY 148

Hurricane Rina has been reduced to a category 1 hurricane today, and never did reach major hurricane status last night. There is no real smoking gun on the evidence list that caused this rapid deterioration. It is most likely a combination of small changes to several variables that added up to one big blow. The most noticeable wound is to her feeder system. The banding features are nearly gone, indicating that she has been having troubles pulling in the moister around her.   

(Hurricane Rina)
Wind shear has remained at moderate levels according to CIMSS shear analysis, and Rina certainly doesn't have the appearance of a sheared system. But it is possible that wind shear is partially responsible for the erosion of the feeder bands. Upper level wind shear looks to have disrupted her exhaust system as well. Without a proper outflow, surface pressures will stop falling. There is no evidence of dry air being injected into Rina's core, and the dry air to the north has actually receded a bit. But that dry air could have played a role in the erosion of the outer edges of Rina. 

(Hurricane Rina Water Vapor Loop)
It is also possible that turbulent land/sea breeze interaction is also tampering with Rina now that she has moved so close to land. One thing that is still in Rina's favor is that her inner core seems to still be in tact. As long as she has that, she can still experience brief periods of strengthening. Her strongest days are probably behind her now though, it would be a huge surprise if she is able to build back up to 110 mph sustained winds. The environmental conditions are expected to remain the same for tomorrow as she approaches Cozumel, so she may fluctuate between 75 and 95 mph sustained until landfall. Although it is starting to look like she might make landfall just a bit further south of her forecast, which means more time over land. That could very well mean the end for this small, struggling storm. That is good news for residents in the Yucatan, as just last night they were bracing themselves for the possibility of a major hurricane landfall.

(Hurricane Rina Microwave Image)
The only other variable would be ocean temperature. We know that slow moving hurricanes can cool sea surface temperatures below. But that is rarely an issue in the Caribbean, where the waters are warmer at depth. But our satellites can't get a good measurement with cloud cover blocking their signal, and there is not a buoy located under Rina at her current position. So we really don't know how ocean temps are affecting her right now.

The Hurricane Center is now forecasting a weaker hurricane to still hit Cozumel tomorrow night. Then the NHC forecast track turns Rina to the east and hooks her to the south near the western edge of Cuba. The 18z model runs actually showed a consensus among the GFS, HWRF and even the GFDL which has finally moved in line with the others showing that hook to the south. 

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