Friday, July 23, 2010

Tropical Depression Bonnie: July 23, Update B

Crossing Florida just took the steam out of this wee Bonnie lass ;-).
She's back to being a Tropical Depression with maximum sustained winds of 35 mph and central pressure of 1009mb. There are pockets of heavy rainfall, but most of the really stong convection (thunderstorms etc) vanished once she was over land and away from the Florida Current. Wind shear has been more-or-less consistent from the south-southeast all day, so the convective activity remained north-northwest of the center.
She sped across the state in about 5.5 hours and is now leaving the west coast via Naples. Her current position is near 26.2N, 81.9W and she's still moving WNW at a rapid 18 mph. She has consistently remained on the northern edge of the cone with almost every advisory, which is why she's farther north than the forecast from a couple of days ago (hence avoiding the Keys). If this continues, whatever is left of her will make landfall in Alabama or possibly Florida again - along the Panhandle (just what you need Pensacola, isn't it?).
I don't anticipate much development over the Gulf, although the surface waters are a warm 29-30 deg C. There are a number of factors that I think will act against any further development. First, she is moving very quickly, so the time over warm water is reduced. Second, she won't be anywhere near the Loop Current <science alert... see below>, and will be mostly over the West Florida Shelf, which is a broad and shallow shelf and the warm water is not very deep. And thirdly, it looks like wind shear will increase even further. The only thing to really keep an eye on is the vorticity (circulation), which is still quite strong in the lowest part of the troposphere.
<Science alert> The Loop Current in the Gulf of Mexico becomes the Florida Current, which in turn becomes the Gulf Stream - kinda like a long windy road that changes name at major intersections. And before it becomes the Loop Current in the Gulf, it is the Yucatan Current in the Caribbean. Crossing any part of this long ocean current system is dicey for storms because the warm water is veerrry deep. A storm churns up water, but when it crosses these areas it churns up more warm water instead of cold water, so it has more 'fuel' and lo-and-behold, convection increases. We saw this in action today when convective activity really picked up as it crossed from the Bahamas to the south east coast of Florida. <End of science alert>.
Notes from the trenches: 
- Marathon (in the Keys) - this afternoon they had lovely blue skies and 5mph winds - from Gene S.
- Miami was wet, but not as bad as the stuff Puerto Rico had - from Chris M. (who is having a rather soggy moving day, but they are leaving Florida so getting hit by a weak Tropical Storm seems a fitting farewell).

And sent in from Richard S.:
    My Bonnie lies over FLO-RI-DA,
     My Bonnie lies over MEEE.
      My Bonnie lies over FLO-RI-DA,
       So send Bonnie back out to Sea!!
Done. :-)
To wrap up the blob in the western Gulf of Mexico story: it produced a lot more rain and thunder than Bonnie, but it's over land, so no blob.
That's all for today. 
Toodle pip!

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These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I was there and was going to "run away, run away" (Monty Python), I'll let you know.

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