[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 020240
TCDAT2

Tropical Storm Larry Discussion Number   6
NWS National Hurricane Center Miami FL       AL122021
1100 PM AST Wed Sep 01 2021

Larry's strengthening phase appears to have taken a pause this
evening.  While an earlier 2055 UTC GMI microwave overpass indicated
that the low-level structure was fairly impressive with a tight
low-level eye-like feature, the deep convection waned briefly, but
has since returned in a band around the eastern portion of the
circulation.  The various satellite-based intensity estimates
have an unusually large spread from about 45 to 75 kt this evening.
At the higher end of the estimates are UW/CIMSS ADT T-numbers of
T4.5 and at the lower end were scatterometer wind data showing peak
wind retrievals of about 45 kt.  But given the small-inner core
seen in the microwave data, there is likely some undersampling
occuring with the ASCAT instrument.  Subjective Dvorak data
T-numbers from both TAFB and SAB were T3.5 (55 kt), and the latest
SATCON estimate is 57 kt.  The NHC initial intensity estimate leans
toward the subjective Dvorak numbers and SATCON, and therefore
remains at 60 kt, but there is larger-than-normal uncertainty
regarding the initial intensity at this time.

Larry is moving westward or 275/18 kt. The track forecast
philosophy has not changed this evening. Larry is expected to move
around the south and southwestern portion of a strong mid-level
ridge that is anchored over the east-central Atlantic. This should
steer the tropical cyclone steadily westward to west-northwestward
during the next few days, with a turn toward the northwest by days
4 and 5 as Larry nears the southwestern portion of the ridge.  The
latest model envelope is largely unchanged through 120 hours, and
the updated official forecast is very similar to the previous
advisory.  Although the track guidance is fairly tightly clustered
there are some differences in how fast Larry will move across the
tropical Atlantic, with the UKMET depicting the fastest forward
speed. The NHC track forecast is slightly slower than the consensus
aids to be in better agreement with the bulk of the guidance and
the GFS ensemble mean.

Conditions are expected to remain favorable for steady to rapid
strengthening.  Despite the recent pause in intensification,
Larry is likely to resume strengthening later tonight, and the
short-term portion of the intensity forecast is unchanged from
before. Larry is forecast to become a hurricane by Thursday
morning, and a major hurricane in 36-48 hours.  That portion of
the intensity forecast is in good agreement with the SHIPS guidance
and is supported by the global model guidance which significantly
deepen Larry over the next couple of days.  After that time, there
are some mixed signals on the amount of shear over the system
with the GFS-based SHIPS guidance predicting moderate shear and some
dry air, while the ECMWF-based SHIPS model diagnoses more favorable
conditions. For now, the NHC intensity forecast shows a peak
slightly higher than before by 72 hours, and then indicates little
overall change in strength thereafter as some fluctuations in
intensity could occur due to eyewall replacement cycles.  The latter
portion of the forecast is in best agreement with the HFIP corrected
consensus aid.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0300Z 12.8N  30.9W   60 KT  70 MPH
 12H  02/1200Z 13.0N  33.3W   70 KT  80 MPH
 24H  03/0000Z 13.6N  36.5W   85 KT 100 MPH
 36H  03/1200Z 14.2N  39.5W   95 KT 110 MPH
 48H  04/0000Z 15.1N  42.2W  100 KT 115 MPH
 60H  04/1200Z 16.2N  44.8W  105 KT 120 MPH
 72H  05/0000Z 17.4N  47.3W  110 KT 125 MPH
 96H  06/0000Z 20.1N  51.4W  110 KT 125 MPH
120H  07/0000Z 22.9N  55.0W  110 KT 125 MPH

$$
Forecaster Brown
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