921 WTPA41 PHFO 010234 TCDCP1 Tropical Storm Iona Discussion Number 20 NWS Central Pacific Hurricane Center Honolulu HI CP012025 Issued by NWS National Hurricane Center Miami FL 500 PM HST Thu Jul 31 2025 Satellite imagery indicates that convection associated with Iona remains disorganized, with warming cloud tops now near -70 C, but still positioned over the low-level circulation center despite ongoing moderate west-northwest shear. However, an earlier ASCAT pass supported peak winds near 40 kt in the northern semicircle, and a blend of the latest subjective Dvorak current intensity estimates continues to support holding the initial intensity at 45 kt. The initial motion is estimated at 285/20 kt. Iona is expected to continue moving west-northwestward during the next couple of days, with a gradual decrease in forward speed as it remains steered along the southern periphery of a low- to mid-level subtropical ridge to the north. A turn toward the northwest is forecast late this weekend through early next week as the system approaches a weakness in the ridge. The updated track forecast has been adjusted slightly to the right of the previous forecast and represents a blend of the prior track and the latest consensus guidance. Very little change was made to the intensity forecast, as most guidance generally holds Iona’s strength steady through the weekend while it begins to turn northwestward and interacts with an upper-level trough. Vertical shear may relax somewhat after 24 hours, which could allow the system to briefly maintain or even slightly increase in strength. However, there is considerable uncertainty regarding how the interaction with the trough will evolve, as small differences in positioning could either support modest strengthening or accelerate weakening. Due to this uncertainty, the intensity forecast maintains Iona as a tropical storm through the weekend, followed by gradual weakening and possible degeneration into a remnant low by the middle of next week. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 13.7N 172.7W 45 KT 50 MPH 12H 01/1200Z 14.3N 175.0W 45 KT 50 MPH 24H 02/0000Z 15.1N 177.9W 45 KT 50 MPH 36H 02/1200Z 16.1N 179.4E 45 KT 50 MPH 48H 03/0000Z 17.2N 177.2E 45 KT 50 MPH 60H 03/1200Z 18.4N 175.1E 45 KT 50 MPH 72H 04/0000Z 19.6N 172.9E 35 KT 40 MPH 96H 05/0000Z 22.8N 168.7E 30 KT 35 MPH 120H 06/0000Z 27.6N 165.5E 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Gibbs (CPHC)
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