ZCZC MIATCDEP3 ALL TTAA00 KNHC DDHHMM Hurricane Calvin Discussion Number 17 NWS National Hurricane Center Miami FL EP032023 1100 AM HST Sat Jul 15 2023 The satellite appearance of Calvin has shown some ill effects today from cooler SSTs and some drier air in its surrounding environment. A 1512 UTC SSMIS 89 GHz passive microwave image of the hurricane showed the eyewall was open to the east, where a dry slot was noted earlier wrapping around that portion of the circulation. Since then, the eye has become a bit warmer and more pronounced in infrared satellite imagery, and some deeper inner-core convection has wrapped around the center. The latest objective and subjective satellite intensity estimates range from 77-90 kt. Based on a blend of these data and recent satellite trends, the initial intensity is held at 85 kt for this advisory. Weakening is expected during the next few days as the cyclone moves into a drier and more stable air mass over sub-26C SSTs. In fact, model-simulated satellite imagery from the GFS and ECMWF suggest Calvin could lose most, or briefly all, of its convection once it enters the central Pacific basin. However, the underlying SSTs become slightly warmer between 48-96 h while the deep-layer shear diagnosed by the global models is low to moderate. Therefore, it seems that Calvin could regenerate new bursts of convection on its approach to Hawaii, which is shown by the global and hurricane models. Therefore, the NHC forecast keeps Calvin a tropical cyclone through 96 h. Regardless of its status, the cyclone appears likely to maintain some tropical-storm-force winds in the northern portion of its circulation as it approaches Hawaii. The global model fields suggest the system will be close to opening into a trough by or shortly after day 5. The long-term motion of Calvin is westward at 280/14 kt. 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. 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. The various track models continue to bring Calvin near or over the Big Island of Hawaii, but exactly where it will track relative to the island is still unclear given the cross-track spread noted at day 3 and beyond. The updated NHC forecast has been adjusted slightly faster than the previous one, but otherwise very little change was made. 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 15/2100Z 15.0N 130.4W 85 KT 100 MPH 12H 16/0600Z 15.6N 132.7W 75 KT 85 MPH 24H 16/1800Z 16.3N 135.8W 65 KT 75 MPH 36H 17/0600Z 16.8N 139.0W 55 KT 65 MPH 48H 17/1800Z 17.3N 142.5W 50 KT 60 MPH 60H 18/0600Z 17.7N 146.2W 45 KT 50 MPH 72H 18/1800Z 18.3N 149.9W 40 KT 45 MPH 96H 19/1800Z 19.4N 156.8W 35 KT 40 MPH 120H 20/1800Z 20.5N 164.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart NNNN