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Hurricane Larry Discussion Number   8
NWS National Hurricane Center Miami FL       AL122021
1100 AM AST Thu Sep 02 2021

Larry continues to gradually become better organized this morning, 
with a small but cold CDO near the estimated center, and well 
defined curved bands rotating completely around. 
Unfortunately, there have not been any recent microwave 
passes over the center in the last 6-9 hours. However, I 
did receive a helpful ASCAT-B pass at 1128 UTC which indicated that 
while the inner core remains quite small, the 34-kt wind radii have 
expanded dramatically in all quadrants. The most recent Dvorak 
subjective intensity estimates were both CI 4.0/65 kt from SAB and 
TAFB. However, the objective intensity estimates from SATCON and 
ADT are higher, at 70 kt and 77 kt respectively. Thus, the current 
intensity of Larry was nudged upward to 70 kt for this advisory.
 
The hurricane's heading has changed little this morning, estimated 
at 280/15 kt. There also remains little change to the forecast track 
reasoning. A dominant mid-level ridge is located north of Larry 
and should maintain the hurricane on a west to west-northwest 
heading over the next 72 hours. The track guidance is in excellent 
agreement over this time period. After 72 hours, a bit more track 
guidance spread begins to take shape, which appears related to the 
evolution of the the steering ridge orientation. For example, the 
most recent GFS run begins a more pronounced rightward bend, as the 
ridge becomes positioned northeast of the tropical cyclone. In 
contrast, the ECMWF and a number of its left-leaning ensemble 
members maintain more ridging directly north of Larry, keeping the 
hurricane on a more leftward track with only a gradual bend to the 
west-northwest and northwest. These differences notwithstanding, the 
consensus aids has changed little from the previous forecast cycle, 
and the NHC forecast track is nearly identical to the previous 
track. This track lies very close to the HCCA consensus aid, which 
favors a track solution a bit closer to the ECMWF versus the GFS.
 
Larry's environmental conditions appear very favorable for 
additional intensification over the next 60-72 hours. In fact, the 
primarily forecast challenge relates to how Larry's core structure 
evolves over the next several days. Right now, the inner-core and 
hurricane-force wind radii are very small relative to the expanding 
tropical-storm-force wind field around the storm. Thus, it appears 
likely that Larry will undergo some form of an eyewall replacement 
cycle (ERC) in the next 12 to 24 hours, which may slow down the 
short term intensification rate. However, once this cycle is 
complete, very light easterly vertical wind shear between 2-8 kt, 
abundant mid-level moisture, and sufficently warm sea-surface 
temperatures between 27-28 C should favor steady to rapid 
intensification. The latest NHC intensity forecast now calls for a 
peak intensity of 120 kt in roughly 72 hours, which is a faster and 
slightly higher peak than the prior forecast. Afterwards, the 
guidance is a bit conflicted. The GFS-based SHIPS continues to 
suggests low vertical wind shear through the end of the forecast 
period. However, the ECMWF-based SHIPS shows much higher 
southwesterly vertical wind shear beginning in 84 hours as Larry 
also moves into a drier environment. It is also possible additional 
ERCs may occur in the latter portion of this forecast, resulting in 
additional intensity fluctuations. For these reasons, the intensity 
forecast at the end of the period shows some modest weakening. This 
intensity forecast is a bit higher than the HCCA corrected consensus 
aid, but remains lower than some of the more aggressive guidance 
(COAMPS-TC, the experimental HAFS-B).  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  02/1500Z 13.5N  34.2W   70 KT  80 MPH
 12H  03/0000Z 13.8N  36.7W   75 KT  85 MPH
 24H  03/1200Z 14.4N  39.7W   85 KT 100 MPH
 36H  04/0000Z 15.3N  42.6W   95 KT 110 MPH
 48H  04/1200Z 16.5N  45.2W  105 KT 120 MPH
 60H  05/0000Z 17.9N  47.6W  115 KT 130 MPH
 72H  05/1200Z 19.2N  49.7W  120 KT 140 MPH
 96H  06/1200Z 21.8N  53.1W  115 KT 130 MPH
120H  07/1200Z 24.6N  56.0W  110 KT 125 MPH
 
$$
Forecaster Papin
 
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