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Major Hurricane Delta


hlcater
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Divergence aloft is just crazy right now. The atmospheric uplift over high heat content is going to continue allowing Delta to fight even the very strong mid level directional shear vector. That being said, as soon as the shear begins to abate, it could rapidly recore and expand. I think it's way too quick to give up on the potential here. Not that anyone is doing that. This may still go bananas NW of the Yucatán by the time it reaches the west-central GOM. If shear backs down a little faster tomorrow, it could even start reintensifying just prior to landfall near the NE Yucatán. But there is no doubt intensification tonight is off the table and also any chance of a Cat 5. If nothing else, a rare micro-cane Cat 4 without a clear eye but reliant on a very small extreme convective eyeband. Without recon or obs, we'd have never known it based on satellite alone.

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4 minutes ago, CoastalWx said:

Seems like the outer cirrus is ever so slightly trying to expand east a bit and maybe an eye trying to pop. 

No eye will form with that linear band cutting the storm in half.     GFS  eventually wraps it around the storm but not until after landfall as it's moving back into the gulf.   You can see the evolution in the 500mb rh fields. 

https://www.pivotalweather.com/model.php?m=gfs&p=500rh&rh=2020100618&fh=12&r=caribbean&dpdt=&mc=

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Still Cat 4 at 11

BULLETIN
Hurricane Delta Advisory Number  10
NWS National Hurricane Center Miami FL       AL262020
1000 PM CDT Tue Oct 06 2020

...EXTREMELY DANGEROUS HURRICANE DELTA CONTINUES HEADING TOWARD THE
NORTHEAST COAST OF THE YUCATAN PENINSULA...
...EXPECTED TO BRING A LIFE-THREATENING STORM SURGE AND EXTREME
WINDS...


SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...19.5N 85.1W
ABOUT 135 MI...220 KM ESE OF COZUMEL MEXICO
MAXIMUM SUSTAINED WINDS...130 MPH...215 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...960 MB...28.35 INCHES
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Well, okay, let's not get carried away. If you look at the earlier missions into delta, not every single pass through the eye results in the same measurement of estimated minimum pressure. Dropsondes are used to measure the low level environment. Past missions on various canes show weaker winds in certain pass throughs. It is obviously weaker, pressure is up, and I think folks on here have done well identifying why (mid layer moderate shear). If you look at that shear it's a testament to the ocean temps the storm has been so explosive today and held together-ish. 

Also, I agree with what some have said: this storm isn't over yet. Yeah, it is weaker now. I could see a drop down to cat 3 status with this update (higher pressure, worse sat presentation, lower aircraft and sfmr winds), or if they're being aggressive, high cat 2, but they aren't going to drop it to a 1. They probably won't drop it to a 2 either. If it continues to weaken they'd go to 2 on the 2am advisory. Continuity, also something someone mentioned. Think about the optics of them going down to cat 2, people in Cancun relax, then, shear drops and it intensifies before landfall and they do a late stage upgrade to cat 4. That's not a good thing and why continuity exists. The ocean is warm, storm is strong, it isn't going away.

 

Edit--they dropped it to 130 so still cat 4, but a big 3-hour drop. Generous. Second edit: yeah okay they also said it was generous. Lol.

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Good writeup by Pasch

Hurricane Delta Discussion Number  10
NWS National Hurricane Center Miami FL       AL262020
1000 PM CDT Tue Oct 06 2020

Observations from a NOAA Hurricane Hunter aircraft and conventional 
and microwave satellite imagery indicate that Delta has not 
intensified since earlier today.  The central pressure has risen 
somewhat and the current intensity estimate, 115 kt, is probably 
generous based on flight-level and SFMR-observed surface winds from 
the NOAA plane.  Although the hurricane continues to have very deep 
convection near and over the center, the cloud pattern lacks 
well-defined banding features, and an eye is not evident on either 
geostationary or polar-orbiting satellite images.  Surveillance 
data from the NOAA G-IV aircraft suggest that Delta's circulation 
does not extend as markedly into the upper troposphere as one would 
expect for a major hurricane.  Given the current state of the 
system, not much strengthening seems likely before the center 
reaches northeastern Yucatan tomorrow morning.  Some weakening is 
likely due to the interaction with land during the next 12-18 
hours.  Re-intensification over the southern Gulf of Mexico is 
still expected, but when Delta reaches the northern Gulf, lower 
oceanic heat content is likely to cause at least slight weakening.  
The official intensity forecast is somewhat above most of the model 
guidance, but not much different from the regional hurricane 
models, HWRF and HMON, over the northern Gulf.

Fixes from the aircraft indicate a continued west-northwestward 
motion at just a slightly slower forward speed, 300/14 kt.  The 
track forecast reasoning is basically unchanged from earlier 
today.  Delta should move along and around the southwestern and 
western periphery of a mid-tropospheric anticyclone centered just 
east of Florida for the next couple of days.  Around 72 hours, the 
flow ahead of a shortwave trough over the south-central United 
States should cause the tropical cyclone to turn north-northeastward 
and move across the central Gulf coast late Friday or early 
Saturday.  The official track forecast remains close to the 
dynamical model consensus, TVCA. 


Key Messages:

1. Life-threatening storm surge and potentially catastrophic wind
damage are expected within portions of the northern Yucatan
Peninsula of Mexico beginning tonight. All preparations to protect
life and property should be rushed to completion.

2. Heavy rainfall will affect portions of the Cayman Islands,
western Cuba and the northern Yucatan Peninsula through midweek.
This rainfall could lead to significant flash flooding and
mudslides. The potential for heavy rain, flash and possible minor
river flooding will increase across portions of the central Gulf
Coast, Tennessee Valley, and southeastern United States as Delta
moves inland later this week.

3. There is an increasing likelihood of life-threatening storm surge
and dangerous hurricane-force winds, especially along the coasts of
Louisiana and Mississippi, beginning on Friday. Residents in these
areas should ensure they have their hurricane plan in place and
follow advice given by local officials.  Storm surge and hurricane
watches will likely be issued for portions of the northern Gulf
Coast on Wednesday.


FORECAST POSITIONS AND MAX WINDS

INIT  07/0300Z 19.5N  85.1W  115 KT 130 MPH
 12H  07/1200Z 20.9N  87.1W  115 KT 130 MPH...INLAND
 24H  08/0000Z 22.3N  89.8W  105 KT 120 MPH...OVER WATER
 36H  08/1200Z 23.6N  91.7W  110 KT 125 MPH
 48H  09/0000Z 25.0N  92.7W  115 KT 130 MPH
 60H  09/1200Z 26.8N  92.8W  115 KT 130 MPH
 72H  10/0000Z 29.0N  92.2W  110 KT 125 MPH
 96H  11/0000Z 33.0N  89.8W   50 KT  60 MPH...INLAND
120H  12/0000Z 36.0N  86.0W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Pasch
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Interesting to see the moderate weakening observed by the hurricane hunters this evening with winds now down to 130 mph (just barely Cat 4). However, in the last hour or so, there have been indications of an eye trying to form, which is often a sign of intensification. The Yucatan could use a break, although 130 mph is still a big deal. Beyond there, no real change as the forecast is still for a Cat 3 hurricane to strike the central LA coast Friday night (120-125 mph) - the center of the track has landfall near Marsh Island, just south of Lafeyette and about 100 miles west of New Orleans and 90 miles east of Lake Charles. Let's see if tonight's models make any big moves on track or intensity.  

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