Major Hurricane Isaias

[vortex95]

9 hours ago, GaWx said:

I’m glad the expected last minute weakening verified well saving from a MH landfall, but realize getting cat 1-2 H effects is of course still a big impactful event (I know first hand).
 

 Interestingly per Dr. Knabb, that same strong shear that caused the dramatic weakening just before landfall actually caused the worst of the thunderstorms/wind gusts (solid cat 2 gusts) to be in your area in the NW eyewall (where Stephanie Abrams great coverage was). It’s almost as if the NW eyewall weakening lagged behind. She said she had never seen so much lightning in an eyewall, which typically has limited lightning due to the upper atmosphere being too warm for as much ice in the clouds vs typically much more lightning in outer bands as Dr. Knabb explained.

 I thought TWC coverage was excellent between her, Cantore showing storm surge and sudden shift to warming S winds off Gulf in E eyewall, and Dr. Knabb.

Regarding the LTG frequency,  Isaias was rapidly going PT/ET, and strong baroclinic influences were present before landfall.  Dry air intrusion and wind shear are going to lead to stronger updrafts b/c more CAPE present.  Asymmetries in the circulation are going to result in frontal-type convergence zones, further promoting stronger updrafts

Also, chasers reported it was a "cold" hurricane. Temps along the FL coast were largely below 70 prior to landfall.  That's not your typical tropical environment.

LTG can be frequent in eyewall in an intense HU in the deep tropics.  Recons have reported this many times in strong Cat 4s and Cat 5s.  What happens is that when a TC gets this intense, updrafts in the eyewall, which normally max out just below typical tstm updraft strength, cross the threshold to make it favorable for LTG. 

 

[vortex95]

This SAR image clearly shows a sting jet, which is a characteristic of a PT/ET low pressure, not a TC.  Also, prior to landfall, there was no coherent, focused wind center.  It was quite elongated.  So despite the satellite appearance w/ all the deep convection, structurally one could argue it had transitioned to more PT/ET than tropical prior to landfall.  That sudden jump of pressure up 12 mb to 970 on recon when it has been holding steady 958-960 mb also indicates a rapid change structurally to away from tropical status.  That suggested a distinct cool/dry air penetration into the core (front).  Once that happens, a system is PT/ET.

Note: SAR shows sustained winds max 110 kt.  The SAR tends to have high bias.
https://www.star.nesdis.noaa.gov/socd/mecb/sar/sarwinds_tropical.php?year=2026&storm=AL092026_ISAIAS

I have always said when a system is transitions like this, there should be a ramp down to subtropical status before PT/ET status.  Why not?   If a system can go from ET to ST to tropical, there is absolute no reason to think it can not work the other way.  This is what should have been done for Sandy for its landfall.  A TC rarely goes instant PT/ET in just 6 hr.  It is *process* that takes time.

And I don't want to hear about the messaging issue.  ST storms get names just like tropical storms, and the watches and warnings are the same ST or tropical.  In fact, a few years ago, JTWC started assigning operationally ST status as systems transitioned from TC.