Charles E. Roop giving his own forecasts, weather discussions, photos and adventures for the Starkville, MS area, Florida, and beyond.

Friday, August 26, 2011

Irene Update

Well, Floridians can breathe a sigh of relief as Hurricane Irene has and will move north and away from the state's east coast. Irene still had effects on Florida though as rain bands from the western edge of the storm impacted the east coast areas of central and southern Florida. Wind gusts as high as 30 mph were reported in south Florida Thursday afternoon. It's likely that Florida's east coast will continue to encounter heavy surf and a high rip current threat.

Currently, Irene is east-northeast of Jacksonville, Fla. with winds of 100 mph and moving north (360 degrees) at 12 knots. The odd thing is that the central pressure is 951 mb. The winds seem fairly light with relation to the low central pressure. This could be because of a weak high to the east of Irene, which would lead to a lower pressure gradient and, therefore, lighter winds. [Mets: If I am wrong, please chime in on this]. The intensity has decreased a bit from earlier today, likely due to dry air intrusion into the system from the southeast based on water vapor satellite imagery.

I am not expecting too much change in strength through landfall, which is expected sometime tomorrow morning. Models are in agreement of an mid to upper trough to move through the Great Lakes and move east. This, along with Irene being on the western edge of the ridge, should keep Irene moving north - maybe a little more north-northeast - and make landfall along the Outer Banks of North Carolina. Based on the certainty of the models and time to landfall, I am confident that a landfall near Morehead City, NC is likely. I think Irene could still be a category two or strong category one hurricane at landfall Saturday morning. There could be some slight weakening as dry air entrainment could pose a threat to the TC. Shear doesn't seem to be an issue anytime soon as outflow looks really nice.

The concern is that the storm is relatively large and can have impacts far from Irene's center of circulation. Storm surge is still a concern on the coast along with heavy rain to areas that have received plenty recently. Because of the large population centers in New England, the societal impacts of Irene will be great.

Since my thesis research falls along the lines of TC and tornado relationships, I should elaborate on a possible tornado threat. Tornadoes from TCs tend to develop on the right-front quadrant of the storm. Literature also points out a higher incidence of TC-tornado outbreaks when dry air entrainment and, therefore, steep relative humidity gradients occur (Curtis 2004). This is something I will try to keep my eye on as the hours move on. For now, the SPC has given a Mesoscale Discussion for the Outer Banks. There is not a high enough risk to issue a severe weather watch at the moment, but the conditions for tornado development could increase later tonight, according to their discussion. Still, with this dry air entering the storm and seeing some decent banding taking place north of the center on visible satellite (see above) has me kind of vigilant.

I will have more on Irene later.

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