ZCZC MIATCDEP3 ALL TTAA00 KNHC DDHHMM Hurricane Calvin Discussion Number 18 NWS National Hurricane Center Miami FL EP032023 500 PM HST Sat Jul 15 2023 During the past several hours, the satellite cloud pattern of Calvin has been unsteady, with the eye coming and going and the eyewall cloud top temperatures fluctuating. Overall, though, there has been little change in the organization and the various satellite intensity estimates. Based on this, the initial intensity is again held at 85 kt, which is close to the CIMMS satellite consensus estimate. Calvin is currently over 25C sea surface temperatures, and it should be over 24C water in about 24 h. This should cause weakening during the next 24-36 h. After that time, the sea surface temperatures start to increase under the forecast track, although they are expected to stay below 26C until the system passes near Hawaii. During this period, the vertical wind shear is forecast to be light to moderate. The consensus of the guidance during this time is that Calvin will continue to weaken while producing intermittent bursts of convection, and that is the basis for keeping it a tropical storm. Regardless of how much convection is present, it appears likely that Calvin will maintain tropical-storm-force winds as it passes near the Big Island of Hawaii. After 96 h, stronger shear should cause the cyclone to degenerate to a remnant low pressure area or trough. The initial motion is now 285/15 kt. As in the previous forecast, a westward to west-northwestward motion will continue through the forecast period as the cyclone is steered by a mid-level ridge entrenched over the eastern Pacific. On the forecast track, Calvin is forecast to cross 140W and enter the central Pacific basin on Monday morning and approach the Hawaiian Islands on Tuesday into early Wednesday. There remains some cross-track spread in the models, so while the new forecast track calls for Calvin to pass close to the Big Island of Hawaii it remains unclear exactly how it will track relative to the island. The new forecast track has only minor adjustments from the previous track. KEY MESSAGES: 1. Calvin is forecast to move across the central Pacific Ocean and approach the Hawaiian Islands early next week. It is too early to determine the exact location and magnitude of potential impacts given uncertainties in the track, intensity, and structure of Calvin as it approaches the islands. Interests in Hawaii should closely monitor the latest forecast updates. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 15.4N 132.0W 85 KT 100 MPH 12H 16/1200Z 16.0N 134.3W 75 KT 85 MPH 24H 17/0000Z 16.6N 137.6W 65 KT 75 MPH 36H 17/1200Z 17.1N 140.9W 55 KT 65 MPH 48H 18/0000Z 17.4N 144.4W 50 KT 60 MPH 60H 18/1200Z 17.9N 148.0W 45 KT 50 MPH 72H 19/0000Z 18.4N 151.6W 40 KT 45 MPH 96H 20/0000Z 19.5N 158.5W 35 KT 40 MPH 120H 21/0000Z 20.5N 165.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven NNNN