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Tropical Storm Iselle Discussion Number   3
NWS National Hurricane Center Miami FL       EP142020
800 PM PDT Wed Aug 26 2020

Satellite imagery indicates that a convective burst has formed a 
little closer to the center of Iselle during the past few hours, 
although the circulation remains at least somewhat elongated.  
Various subjective and objective satellite intensity estimates are 
near 35 kt, so that remains the initial intensity.  The imagery, as 
well as model analyses, show that Iselle continues to be undergoing 
strong easterly shear.

Iselle is embedded in a large monsoon gyre, and the southwesterly 
flow on the south side of the gyre should be the main steering 
influence for the next 60 h or so.  This should result in the 
cyclone continuing its current slow motion toward the northeast.  
After that time, the cyclone should separate from the gyre, allowing 
a mid-level ridge to the north and northeast of the system to become 
the dominant steering mechanism.  This should cause Iselle to turn 
to the north, then northwest, then eventually to the west.  The 
track guidance is in good agreement with the general scenario, 
although there is some spread on when and where there turns will 
occur.  The new forecast track is close to the HCCA corrected 
consensus mode and has only minor adjustments from the previous 
forecast.

Present indications are that the current strong shear will persist 
for several days, and after 72 h the forecast track takes the 
cyclone over cooler sea surface temperatures.  Based on this, 
significant strengthening appears unlikely, although short-lived 
spin ups due to convective bursts are possible.  The new intensity 
forecast is unchanged from the previous forecast in showing little 
change of strength for 72 h, followed by weakening to a depression 
and a remnant low.  An alternative scenario is that the shear causes 
Iselle to weaken to a trough at any time during the next 120 h.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0300Z 16.2N 116.2W   35 KT  40 MPH
 12H  27/1200Z 16.7N 115.8W   35 KT  40 MPH
 24H  28/0000Z 17.3N 115.3W   35 KT  40 MPH
 36H  28/1200Z 17.9N 114.7W   35 KT  40 MPH
 48H  29/0000Z 18.6N 114.1W   35 KT  40 MPH
 60H  29/1200Z 19.4N 113.6W   35 KT  40 MPH
 72H  30/0000Z 20.7N 113.7W   30 KT  35 MPH
 96H  31/0000Z 22.5N 115.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  01/0000Z 22.5N 116.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Beven
 
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