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Tropical Storm Ivo Discussion Number   5
NWS National Hurricane Center Miami FL       EP092025
300 PM CST Thu Aug 07 2025
 
Ivo remains a very small tropical cyclone, though an intensifying 
one. Deep central convection continues to burst near the center, 
though the vertical structure of the tropical storm does appear more 
ragged with evidence that the mid-level vortex is tilted to the 
southwest of the low-level center. A helpful Metop-B scatterometer 
pass at 1643 UTC captured the tiny circulation with a max wind 
retrieval of 44 kt. Assuming this instrument undersampled the peak 
winds of the small cyclone, the initial intensity is being raised to 
50 kt for this advisory, also close to the latest objective ADT 
estimate.
 
The tropical storm continues to move quite quickly to the northwest,
with the motion estimated at 305/18 kt. The track forecast reasoning
is similar to earlier, where a strong and extensive mid-level ridge
parked over northern Mexico should keep Ivo moving quickly
west-northwestward to northwestward for the next 24 hours or so. On
this forecast track, Ivo will soon begin pulling away from the
southwestern coast of Mexico. By this weekend, the ridge begins to
weaken some and the guidance also suggests Ivo will start to become
more vertically shallow. A combination of these influences should
result in a westward turn in the track and a slowdown in the forward
motion. The track guidance for this cycle is quite similar to the
prior one, and the NHC track forecast is largely an update from
the previous one, blending the consensus aids HCCA and TVCE.
 
The intensity forecast presents a conundrum this afternoon. Ivo has 
a small inner core wind field, is over warm 29-30 C ocean waters, 
and vertical wind shear as diagnosed by SHIPS guidance is low, only 
5-10 kt. Ordinarily these variables would suggest that Ivo could 
undergo a period of rapid intensification (RI), and EC-SHIPS-RI 
guidance now has a 71 percent chance of a 30-kt increase over the 
next 24 h. However, other RI indices are lower, with DTOPS at only 
12 percent for the same threshold. There is also evidence that Ivo's 
structure is not ideal, with current visible satellite imagery 
suggesting its circulation is tilted southwest with height. This 
vertical tilt also matches the structure seen in the most recent 
HAFS-A/B model grids. This may explain why the regional-hurricane 
models are less aggressive with Ivo's intensification than SHIPS, 
and only HAFS-B briefly makes Ivo a hurricane. Thus the NHC 
intensity forecast is not as aggressive as the latest SHIPS 
guidance, only taking Ivo to a 70 kt hurricane in 24 hours. 
Thereafter, the storm will cross a sharp sea-surface temperature 
gradient, which should lead to weakening after 24 hours. Like the 
previous forecast, Ivo will likely lose its organized deep 
convection west of Baja California in about 72 hours, where the 
latest forecast shows it becoming a post-tropical remnant low. The 
NHC intensity forecast is a little above the reliable HCCA aid, but 
is lower than both SHIPS and LGEM aids.
 
Given the small radius of tropical-storm-force winds associated with
Ivo, these winds are expected to remain offshore as it begins to
move away from Mexico by tonight. However, heavy rain and rough surf
are likely to occur along portions of the southwest coast of Mexico
during the next day or so.  Outer bands of Ivo are expected to
produce locally heavy rainfall in portions of the Mexican states of
Guerrero, Michoacan de Ocampo and Colima through Friday where flash
flooding is possible.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  07/2100Z 18.8N 105.8W   50 KT  60 MPH
 12H  08/0600Z 20.1N 108.2W   60 KT  70 MPH
 24H  08/1800Z 21.1N 110.9W   70 KT  80 MPH
 36H  09/0600Z 21.5N 112.8W   65 KT  75 MPH
 48H  09/1800Z 21.6N 114.1W   55 KT  65 MPH
 60H  10/0600Z 21.7N 115.8W   40 KT  45 MPH
 72H  10/1800Z 21.9N 117.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  11/1800Z 22.5N 121.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  12/1800Z...DISSIPATED
 
$$
Forecaster Papin
 
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