000 WTPA41 PHFO 221500 TCDCP1 Tropical Depression One-C Discussion Number 1 NWS Central Pacific Hurricane Center Honolulu HI CP012024 500 AM HST Thu Aug 22 2024 The area of low pressure well east-southeast of the Hawaiian Islands has become better organized overnight, with persistent deep convection now over the low-level circulation center. As a result, the first Tropical Depression of the season has formed in the Central Pacific basin. Subjective Dvorak intensity estimates came in at 2.5 PHFO and 1.5 SAB. Taking a blend of these estimates, the initial intensity will be set at 30 knots. The initial motion of Tropical Depression One is set at 270/12 knots. This general motion is expected to continue during the next several days as the system is steered by a large subtropical ridge to the north. A decrease in forward speed and a slight turn toward the west- northwest is forecast by days 4 and 5 as a weakness develops in the subtropical ridge to the north. The track forecast is closely aligned with the consensus guidance. Tropical Depression One is forecast to remain in a low to moderate vertical wind shear environment, with warm sea surface temperatures of 27 to 28C, and adequate deep layer moisture during the next several days. This should result in gradual strengthening of the system as it tracks steadily westward, and a tropical storm will likely form later today. By late in the weekend into early next week, the tropical cyclone will begin to see an increase in westerly vertical wind shear and the potential for some entrainment of drier mid-level air. This should lead to a gradual weakening of the system. The intensity forecast is close to the intensity consensus during the next several days, bringing the system up close to hurricane strength over the weekend, then is slightly lower than the consensus guidance by days 4 and 5. KEY MESSAGES: 1. Tropical Depression One is forecast to approach the Hawaiian Islands during the next few days, bringing the potential for heavy rainfall, along with dangerous surf and rip currents. A Tropical Storm Watch could be required for portions of the main Hawaiian Islands tonight or Friday. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 15.4N 140.8W 30 KT 35 MPH 12H 23/0000Z 15.6N 142.6W 35 KT 40 MPH 24H 23/1200Z 15.8N 145.0W 40 KT 45 MPH 36H 24/0000Z 16.0N 147.5W 45 KT 50 MPH 48H 24/1200Z 16.2N 150.1W 55 KT 65 MPH 60H 25/0000Z 16.6N 152.6W 60 KT 70 MPH 72H 25/1200Z 16.8N 154.8W 60 KT 70 MPH 96H 26/1200Z 17.3N 158.0W 60 KT 70 MPH 120H 27/1200Z 18.4N 161.3W 50 KT 60 MPH $$ Forecaster Jelsema