Tropical Cyclone Discussion

597
WTPZ44 KNHC 242032
TCDEP4
 
Tropical Storm Iselle Discussion Number   6
NWS National Hurricane Center Miami FL       EP092026
200 PM PDT Mon Aug 24 2026

Iselle's cloud pattern continues to gradually improve in 
geostationary satellite imagery despite the moderate 
west-northwesterly shear in the environment.  The cyclone contains a 
core of deep convection with an impressive trailing curved band 
extending southward on the east side of Iselle.  Some recent 
microwave satellite overpasses show a similar structure.  The latest 
subjective Dvorak classification from TAFB is T3.5/55 kt, and 
objective satellite intensity estimates range from 55 to 59 kt.  
Based on the improving structure, the initial intensity is increased 
to 60 kt for this advisory.
 
The initial motion estimate is unchanged from the previous advisory, 
northwestward, or 310/11 kt.  A mid-level ridge north of Iselle is 
forecast to strengthen, causing Iselle to turn west-northwestward on 
Tuesday, and that motion should then continue through the end of the 
week.  The latest NHC track forecast is quite similar to the 
previous one, and lies very close to the HFIP Corrected Consensus 
(HCCA) and the Google DeepMind Ensemble Mean (GDMI).
 
Iselle remains over warm waters and within a moist environment. 
However, the cyclone is experiencing moderate west-northwesterly 
vertical wind shear.  Water temperatures and moisture will remain 
quite favorable for another 12 to 24 h, but the shear is forecast to 
increase slightly to about 20 kt in about 12 h.  Given the recently 
improving structure, the NHC forecast continues to call for the 
system to strengthen to a hurricane in 12 h.  The NHC intensity 
forecast is near the high end of the guidance suite for the first 36 
h of the forecast.  Beyond 24 h, gradually decreasing ocean 
temperatures and moisture will lead to steady weakening, and the NHC 
intensity forecast lies in the middle of the guidance envelope from 
hour 48 onward. The latest ECMWF and GFS simulated satellite imagery 
suggest that Iselle could become a remnant low as early as Thursday. 
The time of when Iselle becomes a post-tropical cyclone has been 
moved forward to 72 hours.  After that, the models indicate the 
remnant low opening up into a trough between day 4 and 5.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/2100Z 19.2N 118.0W   60 KT  70 MPH
 12H  25/0600Z 20.1N 119.4W   65 KT  75 MPH
 24H  25/1800Z 20.9N 121.3W   60 KT  70 MPH
 36H  26/0600Z 21.4N 123.2W   55 KT  65 MPH
 48H  26/1800Z 21.9N 124.9W   45 KT  50 MPH
 60H  27/0600Z 22.4N 126.8W   35 KT  40 MPH
 72H  27/1800Z 22.9N 128.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  28/1800Z 23.5N 133.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  29/1800Z...DISSIPATED