263 WTPA41 PHFO 010836 TCDCP1 Tropical Storm Iona Discussion Number 21 NWS Central Pacific Hurricane Center Honolulu HI CP012025 Issued by NWS National Hurricane Center Miami FL 1100 PM HST Thu Jul 31 2025 Satellite imagery indicates that convection associated with Iona remains fragmented and poorly organized, with the low-level circulation center nearly exposed or located near the western edge of the deep convection due to persistent west-northwest shear. A recent AMSR2 microwave pass revealed an elongated low-level structure oriented from north to south, with no well-defined core. Subjective Dvorak current intensity estimates from HFO, SAB, and JTWC ranged from 2.5/35 kt to 3.0/45 kt. Based on these estimates and the poor satellite presentation, the initial intensity is lowered to 40 kt. The initial motion is estimated at 285/16 kt. Iona is expected to continue moving west-northwestward over the next couple of days while gradually slowing, steered along the southern periphery of a subtropical ridge to the north. A turn toward the northwest is forecast by late this weekend or early next week as the system approaches a weakness in the ridge. The updated track forecast remains close to the previous one, with a slight rightward adjustment that aligns with the consensus guidance. Little change in intensity is expected over the next day or two, but a steady weakening trend should begin by Sunday as the system interacts with an upper-level trough and entrains mid- to upper-level dry air. Most dynamical guidance suggests that Iona will gradually open into a trough by early next week. As such, the official forecast now shows the system dissipating by 96 hours, or Tuesday. This forecast assumes Iona will maintain sufficient convection to remain a tropical cyclone through the weekend. If convection fails to persist, however, dissipation could occur sooner than currently indicated. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 14.2N 174.4W 40 KT 45 MPH 12H 01/1800Z 14.8N 176.7W 40 KT 45 MPH 24H 02/0600Z 15.8N 179.6W 40 KT 45 MPH 36H 02/1800Z 17.0N 177.9E 40 KT 45 MPH 48H 03/0600Z 18.1N 175.7E 35 KT 40 MPH 60H 03/1800Z 19.5N 173.6E 35 KT 40 MPH 72H 04/0600Z 21.3N 171.4E 30 KT 35 MPH 96H 05/0600Z...DISSIPATED $$ Forecaster Gibbs (CPHC)
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