Tropical Cyclone Discussion

639
WTPZ44 KNHC 231446
TCDEP4
 
Tropical Storm Iselle Discussion Number   1
NWS National Hurricane Center Miami FL       EP092026
800 AM MST Sun Aug 23 2026

The area of low pressure that we have been monitoring for the past 
several days (EP92) has had gale-force winds and sufficiently 
well-organized convection for the past 12 h or so.  The ASCAT-C pass 
from 23/0517Z showed winds of 40 kt, and that the system did not yet 
have a well-defined circulation, although it was closer than it was 
on the previous pass from 12 h earlier.  An OSCAT pass a couple 
hours later around 23/0716Z suggested that the surface circulation 
was continuing to become better-defined.  Since that time, satellite 
imagery indicates continued consolidation of deep convection over 
the low-level center, and the system very likely has a well-defined 
circulation by now.  Thus, EP92 is upgraded to Tropical Storm 
Iselle, and the current intensity is estimated at 40 kt based on the 
scatterometer data.

There have been no other recent microwave passes, and the confidence 
in the initial position is low. The initial motion is estimated to 
be west-northwestward, or 300 degrees at 10 kt.  A northwestward 
motion is expected through Monday while Iselle is steered by ridging 
over the southwestern United States and northwestern Mexico. As the 
ridge builds in a bit more to the north of the cyclone, a gradual 
turn toward the west-northwest is expected on Tuesday and Wednesday. 
 The NHC track forecast closely follows the HFIP Corrected Consensus 
(HCCA) model and the Google DeepMind (GDMI), which is on the 
northern side of the guidance envelope.  There is a healthy amount 
of spread in the track guidance, and confidence in the track 
forecast is slightly below average.

Iselle will be traveling over warm water and within a moist 
environment with weak vertical wind shear for the next couple of 
days.  Only slow intensification is forecast during the next 12 h as 
the cyclone attempts to consolidate and form a core.  Given the 
favorable environment, steady strengthening is forecast tonight and 
Monday, and the NHC forecast shows Iselle reaching hurricane 
strength Monday night.  By Tuesday night, a modest increase in 
west-southwesterly vertical wind shear and decreasing sea-surface 
temperatures along Iselle's path should lead to gradual weakening.  
The NHC intensity forecast lies near the intensity consensus and the 
hurricane regional model solutions.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/1500Z 15.3N 114.2W   40 KT  45 MPH
 12H  24/0000Z 16.5N 115.6W   45 KT  50 MPH
 24H  24/1200Z 17.9N 117.2W   55 KT  65 MPH
 36H  25/0000Z 19.3N 118.7W   65 KT  75 MPH
 48H  25/1200Z 20.5N 120.3W   65 KT  75 MPH
 60H  26/0000Z 21.4N 121.9W   60 KT  70 MPH
 72H  26/1200Z 22.0N 123.6W   55 KT  65 MPH
 96H  27/1200Z 23.0N 127.2W   45 KT  50 MPH
120H  28/1200Z 23.9N 130.8W   35 KT  40 MPH