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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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