All eyes are on Tropical Storm Darby, and the forecast details are highly dependent on its eventual track and intensity as it approaches the islands. Unfortunately, a track more on left side of the Central Pacific Hurricane Center (CPHC) forecast cone would result in a much greater threat of damaging winds and intense rainfall, and possibly to a much larger part of the state.
Stay tuned to the latest from CPHC because adjustments are likely to the forecast as we go along. The peripheral moisture from Darby will start to bring some showers to windward Big Island tonight and increase on Friday. More significant bands of heavy showers and squalls associated with Darby are likely to start Friday night, then increase in intensity and frequency as the tropical storm gets closer.
Thus, we have issued a Flash Flood Watch that includes Maui and the Big Island for now. It is very possible we may have to expand the watch to include more areas if the CPHC track continues to shift westward. Until Darby gets close, we will see good conditions for getting ready, with typical trade wind weather with passing mainly windward and mauka showers, especially mornings and nights. After Darby passes, moist, humid southeast flow will continue during the first half of next week.
Based on the latest data from Wavewatch III, we have upgraded the High Surf Advisory to a High Surf Warning for the E facing shores of Maui and the Big Island starting at 6 am Friday. Wavewatch III shows longer period swell reaching 13 feet/13 seconds, so we went with surf heights of 12-20 feet for now.
Also raised the east- shore heights in the remaining advisory areas, to 8 to 12 feet. Adjustments may be needed to any of these details based on what Darby eventually does. Currently the High Surf Advisory for the other islands only goes through 6 am Saturday, but it may need to be expanded or extended as we get a better handle on what Darby will do. Winds and seas directly associated with Darby are likely to start increasing over the southeast offshore waters starting tonight, then spreading westward toward the state on Friday.
Winds and seas will begin increasing over the Big Island southeast waters on Friday, and continue spreading through the coastal waters zones near the Big Island and Maui after that. Although the Small Craft Advisory currently only goes through 6 pm Friday, we will likely be replacing that with tropical cyclone headlines today.