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Hurricane Debby


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The vigorous tropical wave that left Africa days ago is now sharpening and becoming more convectively active as it enters the western Atlantic. The signal on guidance has favored tropical cyclone genesis for days now--much closer to the U.S., and the NHC now designates the area as having 60% odds of development in the next week. 

oW5PlN7.png

Originally, the sprawling wave traversed the eastern and central Atlantic devoid of convection due to the presence of strong SAL. While this prevented convection from developing, a combination of low level moisture pooling, high SSTs/OHC, light wind shear, and diminishing influence of SAL has allowed for gradual disorganized convective development, the first step toward TC genesis that's most likely days from now. 

https://tropic.ssec.wisc.edu/real-time/mtpw2/product.php?color_type=tpw_nrl_colors&prod=natl&timespan=120hrs&anim=html5

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The large wave is now draped across the Greater Antilles, and there are numerous questions over the evolution of the wave in the next 5-7 days. First, how does the wave interaction with the Antilles spur or tighten vorticity? The GFS tried to spawn more robust vorticity after interacting with Haiti/DR, while the Euro for the most part has focused an eventual vortex in the convection that is north of the islands. This obviously has track implications. 

Second, how does a developing wave take advantage of what is likely to be a favorable upper level environment closer to the US? Does it develop faster, as the Euro until today suggested, and get pulled northward and then kicked OTS or NE by a developing Midwest trough, or, if things are delayed and track into the Gulf as the GFS suggests, where does it go?

Third, what will be the steering pattern? There's an increasing signal that the steering pattern between an Atlantic ridge and Midwest trough breaks down as the disturbance reaches the east coast or Gulf, creating immense uncertainty on both track and intensity forecasts. 


The bottom line is that there's a lot of uncertainty with the forecast ahead. Ensembles are the way to go as we move forward the next few days to get a sense of the envelope of possibilities--which are very broad as it stands. OTS to a Gulf threat are on the table. The Gulf and SE US should watch this closely. 

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Welp, there it is... The GFS 00Z OP just showed what a hypothetical TC in the EGOM might do if it loops far enough offshore as opposed to over the coast. Not even going to post it. No need. I'm sure you've all seen it by now anyway.

Expect large variations in output intensity from these operational runs from here on out as any slight deviation in TCG position and steering pattern is going to either park the system near-to-over land or offshore, which, of course has huge intensity implications. It's all still very much beyond realistic modeling range and most likely flat wrong. We have no idea what we're going to be dealing with in 4-5 days other than lots of rain for someone.

At any rate, I was half expecting one of these OPs to eventually go nuts if that looping pattern kept showing up. Just please realize these outputs of an intense TC may come and go every so often over the next couple of days, perhaps more, as long as a loop/stall keeps getting simulated, and don't let them get to your head! lol...

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I think the takeaway is as the storm first approaches the coast conditions begin to get very favorable, and continue to be so as the storm stalls.  As @Windspeedsaid land interaction is key.  Upwelling also might become a factor if it gets very intense before the stall

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18 minutes ago, Windspeed said:

Welp, there it is... The GFS 00Z OP just showed what a hypothetical TC in the EGOM might do if it loops far enough offshore as opposed to over the coast. Not even going to post it. No need. I'm sure you've all seen it by now anyway.

Expect large variations in output intensity from these operational runs from here on out as any slight deviation in TCG position and steering pattern is going to either park the system near-to-over land or offshore, which, of course has huge intensity implications. It's all still very much beyond realistic modeling range and most likely flat wrong. We have no idea what we're going to be dealing with in 4-5 days other than lots of rain for someone.

At any rate, I was half expecting one of these OPs to eventually go nuts if that looping pattern kept showing up. Just please realize these outputs of an intense TC may come and go every so often over the next couple of days, perhaps more, as long as a loop/stall keeps getting simulated, and don't let them get to your head! lol...

The part with extreme rainfall somewhere along the Eastern half of the Gulf Coast seems very possible.  I suspect many smaller cities right on the Gulf could handle Harvey-esque rain, but Harvey like rain in New Orleans or Tampa could produce Harvey like rains.  I think a 3 day stall is a fairly low possibility.  GEFS through 6 days are mostly above 1000 mb.

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2 minutes ago, wthrmn654 said:

Early on euro, looks like it lost the storm with nothing out to Monday.

0Z Euro: stays in Gulf through end of run as a weak system; extreme rainfall just off W coast of FL

0Z UKMET: TC into Mississippi that then turns E

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Another consequence of the record warm SSTs on the east side of the Gulf could just as easily be the potential for catastrophic flooding in the vicinity, should this wave get trapped under the ridge. The Gulf on average is just behind last year.

There’s plenty of uncertainty here until we get a persistent consolidation of convection, and I wonder if we see that occur just along the north coast of Hispaniola and/or Cuba given the frictional convergence that would be favored there.

 

image.png

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2 hours ago, purduewx80 said:

Another consequence of the record warm SSTs on the east side of the Gulf could just as easily be the potential for catastrophic flooding in the vicinity, should this wave get trapped under the ridge. The Gulf on average is just behind last year.

There’s plenty of uncertainty here until we get a persistent consolidation of convection, and I wonder if we see that occur just along the north coast of Hispaniola and/or Cuba given the frictional convergence that would be favored there.

 

image.png

Yep in Savanah Ga right now heading to Florida until August 11th.  Water temp 89-92 along west coast. 

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The 6Z GFS is something to behold. 

Genesis off Ft. Myers coast Sunday

High end TS into Nature Coast on Monday

TS off the Savannah coastline Tuesday

CAT 1 well off the Jacksonville coastline Wednesday

CAT 2 hits Jacksonville Thursday

TS over Tallahassee Friday

TS over Tallahassee Saturday 

TS back in GOM south of Cape San Blas on Sunday

TS north of Mobile Bay Monday 

 

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2 hours ago, Seminole said:

The 00Z runs are all over the map. One common theme is frog strangler amounts of rain for Florida. As for the stall over water, I would think upwelling will cap out intensity which the Euro hints at. 

Gotta watch out for those frog stranglers.  Sorry, couldn't resist.  

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