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Tropical Storm Iselle Discussion Number   4
NWS National Hurricane Center Miami FL       EP142020
200 AM PDT Thu Aug 27 2020
 
A sheared band of deep convection has persisted near and to the 
southwest and west of Iselle's center. Night-visible satellite 
imagery indicates that the circulation has tightened up somewhat, 
and the latest UW-CIMSS SATCON intensity estimate is 41 kt. Based 
on these satellite data, the initial intensity has been increased 
to 40 kt. Unfortunately, all three scatterometer passes missed 
Iselle's inner-core wind field.
 
The initial motion estimate is 030/04 kt. Similar to Tropical Storm 
Hernan farther to the east, Iselle is forecast to remain embedded 
within a large monsoon gyre, which will gradually contract down as 
Hernan moves toward southern Baja California and weakens over the 
next few days. This will result in the current southwesterly flow on 
the south side of Iselle to become more southerly, which will 
gradually turn the cyclone northward and then northwestward. By 72 
hours, Iselle is expected to interact with and possibly absorb the 
remnants of Hernan when the two systems are west-southwest of Baja 
California. Thereafter, Iselle is forecast to move westward to 
west-southwestward and slowly weaken. The new NHC forecast track is 
close to a blend of the HCCA corrected-consensus model and the 
simple consensus models GFEX and TVCE, and is similar to the 
previous advisory track.
 
Although short-lived convective bursts near the center will likely 
continue for the next few days, no significant strengthening is 
forecast for the next 48 hours due to moderate-to-strong easterly 
vertical wind shear that will persist across the system. At 60 
hours and beyond, strong shear is expected to gradually weaken 
Iselle, with degeneration into a post-tropical remnant low forecast 
to occur by day 4, with the cyclone possibly even dissipating by 120 
hours. The NHC intensity forecast is similar to the previous 
advisory, and closely follows the IVCN intensity consensus model.

FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0900Z 16.6N 116.1W   40 KT  45 MPH
 12H  27/1800Z 17.2N 115.7W   40 KT  45 MPH
 24H  28/0600Z 17.8N 115.2W   40 KT  45 MPH
 36H  28/1800Z 18.4N 114.6W   40 KT  45 MPH
 48H  29/0600Z 19.3N 114.1W   40 KT  45 MPH
 60H  29/1800Z 20.5N 113.9W   35 KT  40 MPH
 72H  30/0600Z 21.7N 114.6W   35 KT  40 MPH
 96H  31/0600Z 22.4N 115.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  01/0600Z 22.4N 117.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Stewart
 
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