000 WTPA41 PHFO 310843 TCDCP1 Tropical Storm Iona Discussion Number 17 NWS Central Pacific Hurricane Center Honolulu HI CP012025 Issued by NWS National Hurricane Center Miami FL 1100 PM HST Wed Jul 30 2025 Satellite imagery indicates that convection has become more concentrated over the center of Iona, with a recent convective burst producing cloud tops as cold as -85 C. This burst has obscured the previously exposed low-level circulation center, though the overall structure generally remains disorganized. Subjective Dvorak current intensity estimates ranged from 2.5/35 kt (JTWC) to 3.0/45 kt (SAB), with HFO at 3.5/55 kt. These values are mostly consistent with objective satellite intensity estimates, which ranged from 30 to 40 kt. Based on a blend of these estimates and the current satellite presentation, the initial intensity is held at 45 kt. The initial motion is estimated at 280/20 kt. Iona is expected to continue moving westward over the next day or two along the southern periphery of a low- to mid-level subtropical ridge located to the north. By 48 to 60 hours, a gradual turn toward the west-northwest and a decrease in forward speed are anticipated as the system approaches a weakness in the ridge. The forecast track remains consistent with the previous advisory and is well supported by the latest consensus guidance. Only slight additional weakening is expected in the short term as Iona remains embedded within a moderate westerly shear environment of 20 to 25 kt. By around 60 hours (Saturday), vertical shear is forecast to relax, which could allow the cyclone to hold steady or even briefly restrengthen as it moves over slightly warmer waters. However, conditions are expected to deteriorate again late this weekend through early next week, with increasing shear and mid-level dry air likely leading to weakening. The intensity forecast has been held steady from the the previous advisory, supported by the recent burst of convection and the latest guidance. This forecast assumes that Iona will maintain enough convection to remain a tropical cyclone, but if convection fails to persist, the system could degenerate into a remnant low sooner than currently indicated. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 12.3N 166.9W 45 KT 50 MPH 12H 31/1800Z 12.7N 169.8W 40 KT 45 MPH 24H 01/0600Z 13.5N 173.3W 35 KT 40 MPH 36H 01/1800Z 14.1N 176.7W 35 KT 40 MPH 48H 02/0600Z 14.9N 179.6W 35 KT 40 MPH 60H 02/1800Z 15.8N 177.9E 35 KT 40 MPH 72H 03/0600Z 16.6N 175.7E 35 KT 40 MPH 96H 04/0600Z 18.4N 171.3E 30 KT 35 MPH 120H 05/0600Z 20.5N 167.1E 30 KT 35 MPH $$ Forecaster Gibbs (CPHC)
Source link