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Tropical Storm Sonia Discussion Number   7
NWS National Hurricane Center Miami FL       EP182025
200 AM PDT Sun Oct 26 2025
 
After experiencing a late afternoon diurnal minimum in convection on 
Saturday during which the structure of Sonia was rather disorganized 
and the intensification of the tropical storm halted, deep 
convection has returned over the center overnight, with a large area 
of cloud tops colder than -70C.  Light to moderate southerly shear 
appears to be affecting the storm just a bit, with the low-level 
center situated in the southern half of the convective area.  The 
latest subjective intensity estimates are T3.0/45 kt from TAFB and 
T3.5/55 kt from SAB.  The objective UW-CIMSS numbers have been 
running in the 40-45 kt range, and the highest ASCAT vector on a 
recent ASCAT pass was 41 kt.  The initial intensity is held at 45 kt 
based on the above data.
 
Sonia is experiencing about 10-15 kt of southerly vertical wind 
shear while over sea-surface temperatures (SSTs) of about 27C.  The 
shear and SSTs should remain about the same for the next 12-24 h, 
but southerly shear is forecast to increase further after that time 
while SSTs begin to gradually decrease.  By 60 hours, shear should 
be stronger than 20 kt while SSTs fall below 26C.  Melissa will also 
reach a drier airmass after 60 h.  The NHC forecast will show slight 
strengthening over the next 24 h while Sonia remains over lukewarm 
SSTs and moderate shear.  Thereafter, gradual weakening is expected, 
and Melissa should lose its convection and become a remnant low by 
day 3.  The intensity forecast is at the high end of the guidance 
suite through the first 36 hours of the forecast, but shows a 
slightly lower peak intensity compared to the previous NHC forecast. 
The GFS and ECMWF simulated satellite products show the cyclone 
losing its convection between 60-72 h, so the NHC forecast will call 
for Sonia to become a remnant low by hour 72, and gradually 
dissipate thereafter.

Sonia has been moving slightly south of due west (265 degrees) at a 
slow forward speed of 4 kt.  A weakness in a narrow subtropical 
ridge to the north should cause Sonia to turn toward the 
west-northwest later today, but still at a very slow forward speed, 
because the steering currents overall are weak.  By Tuesday, as the 
cyclone weakens, a turn back toward the west with an increase in 
forward speed is expected as Sonia is steered primarily by the low- 
level flow.  The latest NHC forecast is a tad slower than the 
previous prediction and lies generally between the latest HFIP 
Corrected Consensus Approach (HCCA) and Google Deep Mind Ensemble 
Mean (GDMI).
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0900Z 13.4N 119.5W   45 KT  50 MPH
 12H  26/1800Z 13.5N 119.9W   50 KT  60 MPH
 24H  27/0600Z 13.9N 120.6W   55 KT  65 MPH
 36H  27/1800Z 14.3N 121.6W   55 KT  65 MPH
 48H  28/0600Z 14.7N 122.8W   45 KT  50 MPH
 60H  28/1800Z 14.8N 124.3W   35 KT  40 MPH
 72H  29/0600Z 14.9N 126.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  30/0600Z 14.5N 129.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  31/0600Z...DISSIPATED
 
$$
Forecaster Hagen
 
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