844 WTPA41 PHFO 312032 TCDCP1 Tropical Storm Iona Discussion Number 19 NWS Central Pacific Hurricane Center Honolulu HI CP012025 Issued by NWS National Hurricane Center Miami FL 1100 AM HST Thu Jul 31 2025 Iona is still generating a large area of strong but disorganized convection over the low-level center. An earlier partial SSMI/S overpass suggest the convection had poorly-defined banding, and that the low-level center may have become elongated. Satellite intensity estimated have increased a little over the past several hours and now are in the 40-60 kt range. The intensity will be held at 45 kt for now. The initial motion is now 285/19 kt. Iona is expected to continue west-northwestward with a decrease in forward speed for the next two to three days as it moves along along the southern periphery of a low- to mid-level subtropical ridge located to the north. After 60-72 h, the models have come into better agreement than Iona should turn northwestward toward a break in the subtropical ridge west of 160E, with the formerly more westward GFS joining the more northward ECMWF/Canadian. The model guidance envelope has shifted to the right since the last advisory, and while the new forecast track is also shifted to the right it still lies to the left of the center of the envelope and the consensus models. Iona continues to be affected by 20-25 kt of northwesterly shear. This should continue for the next 24 h or so, and during this time the storm is expected to weaken some. Subsequently, the shear is forecast to decrease, but the global models forecast the cyclone to move close to an upper-level low or trough. It is not clear at this time whether this will be favorable or unfavorable for Iona to re-intensify, as small changes in the relative positions of the systems could make a large difference in how much intensification might occur. After 96 h, the global models agree that Iona should weaken, possibly due to upper-level convergence and dry air entrainment. In contrast, the HAFS regional hurricane models forecast re-intensification at that time. Overall, the intensity guidance has trended higher since the last advisory. Due to the uncertainties, the new intensity forecast will not yet make significant changes and is an update of the previous forecast. However, it lies near the lower end of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 13.2N 170.7W 45 KT 50 MPH 12H 01/0600Z 13.8N 173.4W 40 KT 45 MPH 24H 01/1800Z 14.6N 176.6W 35 KT 40 MPH 36H 02/0600Z 15.4N 179.4W 35 KT 40 MPH 48H 02/1800Z 16.4N 178.0E 35 KT 40 MPH 60H 03/0600Z 17.4N 175.8E 35 KT 40 MPH 72H 03/1800Z 18.4N 173.4E 35 KT 40 MPH 96H 04/1800Z 20.8N 169.1E 30 KT 35 MPH 120H 05/1800Z 23.4N 165.3E 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven
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