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Hurricane Isaac, Part 3 - Analysis and Forecasting Thread


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The global models have actually done a pretty job handling the intensity trend the last couple of data with significant organization holding off til today. The GFS shows 925 mob winds increasing about 30 kt between now and LF tomorrow evening, reaching a peak near 100 kt. Will be interested to see how this plays out. To be honest it doesn't need to deepen all that much, the circulation just needs to tighten with a corresponding increase in winds.

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Does anyone know if this is near the record lowest pressure for a tropical storm in the Gulf?

We have seen interesting wind/pressure relationships in recent years from Alex to Ike and Earl to Irene.

Probably Opal, 980mb TS...not counting some that were interacting with land (like Juan 1985, 978 mb), or after landfall.

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I call it annoying not interesting. However this is not uncommon in the wpac so I assume it can happen im our basin. I think isador had a lower pressure

Why does it matter? Not all tropical systems have to magically be 80 mph hurricanes with 980ish pressure.

Given Isaac's size, at 70 it is a significant impact system despite a lower wind max. It not being 75 does not make it any less of a storm.

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In my novice opinion, it looks like outflow was surging east in this shot. I figure it could be related to the sunset and sun angle, but do any pros have anything to say about it?

I feel like it's been working east for a while now....Isaac definitely took a nice shot of dry air before the east side could wrap up but I think it will be the last for the time being.

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Probably Opal, 980mb TS...not counting some that were interacting with land (like Juan 1985, 978 mb), or after landfall.

Opal was another very large tropical cyclone. Of course it had much more time over water when it became a hurricane (54 hours) but it still managed to develop a very tight inner core.

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Why does it matter? Not all tropical systems have to magically be 80 mph hurricanes with 980ish pressure.

Given Isaac's size, at 70 it is a significant impact system despite a lower wind max. It not being 75 does not make it any less of a storm.

IKE rating thus far - will be interesting to watch the surge/wave rating as we move into tomorrow

post-77-0-76171400-1346112633_thumb.jpg

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Probably Opal, 980mb TS...not counting some that were interacting with land (like Juan 1985, 978 mb), or after landfall.

Been thinking about Opal a few times in regards to that storm. That storm basically went ballistic just a few hours before landfall. I believe it got to 150mph before managing the more typical pre-landfall weakening... I think it was a 3 at landfall.

Sent from my Milestone X 2

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Or is it convection the NE weakening? Consider the effects all that convection to the NE could have...

Nice to see you again! I'm using knowledge from severe weather operations, but generally speaking you get a moist environment along and behind the outflow boundary. If this outflow boundary is acting to do just that, it could help us a few hours down the road.

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Irene made landfall at NYC as a strong TS with a pressure of 962mb

Tropical storms weakening from a major hurricane level peak often have pressures that low especially toward higher latitudes.

A TS in the developing stages in the GoM with a min pressure of 981 is pretty uncommon I think ... by no means unprecedented, but still not common

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Been watching the evolution of what looks to my enthusiast eye what seems to be a southern outflow channel that has been associated with convection over the Florida peninsula moving quickly westward toward the south of the core. Would seem that in addition to aadding additional ventilation to the storms SE, the dry air that has been being pumped in on the east side from the ULL to the SW is about to end.

http://www.ssd.noaa....x/flash-wv.html

wv-l.jpg

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FWIW NHC initialized 0Z models as a 60 knot TS, not a HU.

AL, 09, 2012082800, , BEST, 0, 267N, 865W, 60, 981, TS, 34, NEQ, 150, 160, 100, 180, 1008, 230, 30, 0, 0, L, 0, , 0, 0, ISAAC, D,

AL, 09, 2012082800, , BEST, 0, 267N, 865W, 60, 981, TS, 50, NEQ, 50, 60, 50, 40, 1008, 230, 30, 0, 0, L, 0, , 0, 0, ISAAC, D,

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It does look pretty nasty at the end, but I have seen this be overzealous in developing these systems in the past. We'll see, either way I expect this cane will look very nice at some point tomorrow.

Yes, which is why its key to see if its still developing a robust eye at the same period. Heres a nice dprog/dt animation of the last few model cycles. If anything, it has trended stronger as the hour selected here (05z... 1am) is moving closer and closer to real time. The overall forecast motion seems to also be slowing given that its shifted to the south and east form the initial 14 hour forecast.

dprog_dt_hrrr.gif

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