741 WTPA41 PHFO 280840 TCDCP1 Tropical Storm Iona Discussion Number 5 NWS Central Pacific Hurricane Center Honolulu HI CP012025 Issued by NWS National Hurricane Center Miami FL 1100 PM HST Sun Jul 27 2025 The satellite presentation of Iona has improved this evening, with a well-defined curved banding structure and excellent upper-level outflow evident in all quadrants. A recent 28/0650Z Metop-C ASCAT pass showed a few wind barbs near 40 knots. The latest subjective Dvorak current intensity estimates came in at 3.0/45 knots from PHFO, 3.0/45 knots from SAB, and 2.5/35 knots from JTWC. Objective intensity estimates ranged from 42 to 49 knots. Taking a blend of these data, the initial intensity for this advisory has been raised to 45 knots, which may still be slightly conservative. Tropical Storm Iona is moving westward at 270 degrees/10 knots. This general motion is expected to continue over the next several days as the cyclone moves along the southern periphery of a subtropical ridge to the north. A gradual increase in forward speed is also expected, due to a strengthening low- to mid-level ridge north of the system. The track forecast remains closely aligned with a blend of the FSSE, HCCA, and GFEX consensus guidance and is nearly unchanged from the previous advisory. Confidence remains high that Iona will stay well south of the Hawaiian Islands. The environment appears conducive for further intensification over the next day or so, as Iona remains over warm waters near 28C, with adequate mid-level moisture and very light vertical wind shear. In fact, the latest GFS and ECMWF SHIPS guidance indicates more than a 30 percent chance of a 25-knot increase in intensity over the next 24 hours. Given the current structure and favorable conditions, the intensity forecast explicitly calls for rapid intensification during the next 24 hours, with Iona expected to become a hurricane late Monday or Monday night. Iona should reach peak intensity Monday night or Tuesday, with steady weakening anticipated beginning Tuesday night, as the system moves over slightly cooler waters, begins to experience increasing westerly vertical wind shear, and starts to entrain drier mid-level air. The cyclone is expected to become a post-tropical remnant low by Day 5 and could potentially weaken into a trough by that time. The intensity forecast has been raised from the previous advisory to reflect the latest trends in the guidance, and is best aligned with the FSSE and IVCN consensus solutions. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 10.9N 149.3W 45 KT 50 MPH 12H 28/1800Z 10.9N 150.6W 55 KT 65 MPH 24H 29/0600Z 10.9N 152.7W 70 KT 80 MPH 36H 29/1800Z 11.0N 155.1W 75 KT 85 MPH 48H 30/0600Z 11.2N 158.0W 65 KT 75 MPH 60H 30/1800Z 11.6N 161.2W 55 KT 65 MPH 72H 31/0600Z 12.0N 164.8W 45 KT 50 MPH 96H 01/0600Z 12.9N 172.0W 35 KT 40 MPH 120H 02/0600Z 14.5N 179.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Jelsema (CPHC)
Source link