000 WTPA41 PHFO 182039 TCDCP1 Tropical Storm Calvin Discussion Number 29 NWS Central Pacific Hurricane Center Honolulu HI EP032023 1100 AM HST Tue Jul 18 2023 A large area of deep convection developed overnight in the northern semicircle of Calvin's circulation. This convection has persisted through this morning and has obscured the low level circulation center that was so clearly visible yesterday. Fortunately, the US Air Force Reserve has a WC-130J flying a mission into the system today that has helped better identify the system's center and surrounding wind field. SFMR data indicated 46 kt in the NE quadrant and a large area of winds at or above 34 kt. As a result, the initial intensity for this advisory has been increased slightly to 45 kt. The 34 kt radius in the NE quadrant has also been increased as well. The initial motion for this advisory is 280/19 kt as Calvin continues to move south of a subtropical ridge. No significant changes in this steering is expected over the next several days. The main objective aids have the center of Calvin passing south of the Big Island tonight. The track forecast is essentially the same as the previous advisory and is on the northern side of the guidance envelope, but still south of the Big Island. The overall environment around Calvin remains dry and stable. Calvin is currently passing over SSTs of 25-26C. Along the forecast track, SSTs will be gradually increasing and will be 26-27C as Calvin passes the Big Island. Vertical shear affecting the tropical cyclone is expected to be moderate through tonight. The lack of strong vertical shear, and the warmer SSTs should allow Calvin to maintain winds at tropical storm intensities through Wednesday. Shear levels should significantly increase Wednesday night onward, and should result in a weakening to post-tropical/remnant low status on Thursday. KEY MESSAGES: 1. Calvin is forecast to pass very close to Hawaii County tonight, bringing a period of heavy rain, high surf and locally strong winds. Calvin is expected to weaken as it moves westward to the south of the other Hawaiian Islands Wednesday and Wednesday night, bringing the potential for some peripheral impacts. 2. It is important to not focus on the exact forecast track and intensity when preparing for Calvin. Persons in Hawaii County should prepare during daylight hours for impacts prior to the onset of tropical storm conditions, which are expected to start this evening. These impacts could include flash flooding, damaging winds, and large and dangerous surf. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 17.8N 151.9W 45 KT 50 MPH 12H 19/0600Z 18.2N 154.3W 45 KT 50 MPH 24H 19/1800Z 18.8N 158.1W 40 KT 45 MPH 36H 20/0600Z 19.2N 161.8W 35 KT 40 MPH 48H 20/1800Z 19.5N 165.6W 30 KT 35 MPH 60H 21/0600Z 19.8N 169.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 21/1800Z...DISSIPATED $$ Forecaster Kodama