054 WTPZ44 KNHC 072120 TCDEP4 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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