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Tropical Storm Isaac, Part 1: Moving Through The Eastern Caribbean Sea


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8pm advisory confirms a center hop to the WSW. Relocation appears to still be in progress with the H5 low to the SW of the surface low. Funny how these center hops on developing storms can make a huge impact on the eventual track and intensity of the cyclone.

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15.7°N 62.2°W is the given 8pm position, .3 South and 1.0W of 5pm.

I noted that the 18Z GEFS actually lost its more SW members (toward the Yucatan) and gained a few again that go east of FL. Those members seem to go poleward relatively quickly and the fact that the center seems to be reforming more south this evening would seem to go against that idea.

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One negative for a more westward track is the very large size of the projected cyclone. A smaller TC in this sort of environment is much more easily controlled by the mid-level ridge in place. Since Isaac is already so large, the mid-level ridge is eroded more simply because the lower mid-level heights associated with the cyclone.

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The last couple of recon fly-throughs seem to indicate that the center of Isaac is still nudging a bit south of west. Considering that a significant portion of the latitude Isaac is forecast by NHC to gain prior to interaction with Hispanola takes place in the next few hours, I wonder if this short term trend will have some more significant long term impacts.

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Is it possible that what people are referring to in their polarward statement, whether they realize or not, is "beta drift" ??

Perhaps. A stronger storm with stronger windspeeds would have a higher coriolis, and thus more of a beta drift to the NW (as opposed to straight poleward). Not sure if this is to which they are referring, though.

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The last couple of recon fly-throughs seem to indicate that the center of Isaac is still nudging a bit south of west. Considering that a significant portion of the latitude Isaac is forecast by NHC to gain prior to interaction with Hispanola takes place in the next few hours, I wonder if this short term trend will have some more significant long term impacts.

Looking at the way that W-E band of convection currently over and S of Guadaloupe on the 2315Z image is moving west, it would seem pretty clear that at least the circulation driving that motion is to the S or SW, meaning that the center has got to be reforming now pretty well S of 16N.

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I think this SW relocation is very significant. It increases the possibility of 1) missing Shredderola, 2) missing S FL, and 3) impacting a further-N Gulf Coast location with greater intensity.

Exactly. In addition, it looks like there's been a very intense burst of convection right over the center during the last couple of hours. I'd like to see some of that just a bit further south instead of piled on the N/E side of the center, but that convection will hopefully boost Isaac enough so that the E Caribbean/Hispanola don't just shred it into an open wave (not that I see that happening either way).avn0.jpg

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OPERATIONS

Wednesday, Aug 22, 2012

NOAA-42: Is currently flying in Tropical Storm Isaac. This flight took of around 2000 UTC from Barbados and will land in Barbados.

Comments: NOAA42 is flying a P-3 TDR mission. Three HRD scientists will be on this flight.

Thursday, Aug 23, 2012

G-IV: Is scheduled around Tropical Storm Isaac. Take off will be at 1730 UTC from MacDill and will recover at MacDill. The G-IV will be sampling the subtropical ridge north of Isaac. No HRDers will be on this flight.

NOAA-42: Scheduled for a tasked mission into Tropical Storm Isaac. Takeoff will be at 0800 UTC from Barbados and landing in Barbados.

Comments: NOAA42 will fly a P-3 TDR mission into AL94. Three HRD scientists will be on this flight.

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Recon menu for tonight.

-USAF recon just left the system.

-We have the NOAA research mission until 11:30 pm

-USAF recon begins fixes at 1:30 am

-NOAA Research mission begins at 5 am

G-IV synoptic mission is scheduled for 1:30 pm tomorrow

Will the NOAA research mission help tonight's model data, or is it just tomorrow's G-IV?

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Looking at the way that W-E band of convection currently over and S of Guadaloupe on the 2315Z image is moving west, it would seem pretty clear that at least the circulation driving that motion is to the S or SW, meaning that the center has got to be reforming now pretty well S of 16N.

Also interesting to note that this is the first time in quite a while that there's been significant convection on the north and northeast quads (upshear), indicating that perhaps whatever mid-level shear was affecting Isaac earlier may be abating. Assuming the NHC center is correct, the center is pretty well enshrouded in precip on the Guadeloupe radar.

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00z TVCN is due south of Panama City by D5. Models seems to have adjusted due to the new center location.

I hate speculating on the NHC's track, but I would think that an adjustment to the south and west is likely.

EDIT: That TVCA track would be close to the "worst case scenario"

Starting to feel better now that we have -85C tops over the LLC

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