SynopsisModerate trade winds will prevail statewide into Friday. Stable and rather dry conditions will persist over most areas, with a few showers over windward Kauai today and an increase in windward rainfall expected on the Big Island and Maui late tonight and Friday. Winds will shift out of the southeast over the western end of the island chain late Friday and Saturday as a front approaches. The dissipating front will likely fuel increased showers, mainly over windward slopes, during the first part of next week, while high pressure setting up northwest of the state drives breezy and gusty trade winds.
DiscussionA stable a rather dry trade wind flow will dominate over most of the state today. A relatively weak surface high is passing about 300 miles north of the islands, while ridging aloft remains in place. The overnight Hilo sounding and recent aircraft data into hnl show an inversion down between 3500 and 4500 ft, while precipitable water values remain well below an inch. A narrow and diffuse band of shower bearing cumulus clouds, the tail end of a dissipated front, dropped down over Kauai overnight and will remain in place through the morning. As a result, expect low end moderate trade winds to produce some showers over windward Kauai this morning while dry conditions persist elsewhere.
Moderate trade winds will hold into Friday while ridging aloft maintains stable conditions. An area of moisture currently sitting 275 miles east of Hilo will drift westward, bringing an increase in windward rainfall on the Big Island and east Maui late tonight and Friday. Windward rainfall should be minimal elsewhere.
Heading into the weekend, the surface ridge north of the state will strengthen and edge a little closer to the islands. As a result, easterly trade winds over the Big Island and Maui will continue, and could possibly strengthen a notch, while winds shift out of the southeast over Kauai and Oahu. Rainfall will continue to be focused over windward slopes of all islands, though some spotty afternoon showers will be possible over the smaller islands.
An increase in trade winds and periods of active showers on some islands are expected during the first half of next week. Strong high pressure building far northwest of the state will push a dissipating frontal boundary toward the islands on Monday. An increase in rainfall is due on Kauai by Monday night, with the band of moisture likely moving over Oahu and parts of Maui county on Tuesday. The latest GFS and ECMWF guidance shows that trade winds could become strong and gusty on Tuesday and Wednesday, though its too early for details.
AviationVfr conditions will dominate over most areas through at least the evening. The exception will be isol MVFR cigs on windward Kauai, mainly this morning.
MarineThe large northwest swell will continue today. Data from buoy 51001 show the swell holding relatively steady this morning in the 14 to 16 ft range at 14 to 15 seconds. This will maintain warning level surf across most north and west facing shores today, and assuming the decrease in swell energy does not begin until mid day, the high surf warning will have to be extended through the night. The warning will likely be replaced by a high surf advisory for most of the affected areas on the smaller islands for Friday. The next northwest swell is expected to produce advisory level surf on Sunday and Monday.
A small craft advisory /sca/ remains in effect through tonight for most waters due to elevated seas from the large swell. Trade winds may also increase to SCA strength in the typically windy waters around the Big Island and Maui county tonight.
HFO Watches/Warnings/AdvisoriesHigh surf warning until 6 pm HST this evening for north and west facing shores of Niihau Kauai Oahu and Molokai, for north facing shores of Maui, and for west facing shores of the Big Island.
High surf advisory until 6 pm HST this evening for north facing shores of the Big Island.
Small craft advisory until 6 am HST Friday for Kauai northwest waters, Kauai windward waters, Kauai leeward waters, Kauai channel, Oahu windward waters, Oahu leeward waters, Kaiwi Channel, Maui county windward waters, Alenuihaha channel, Big Island windward waters.
Small craft advisory from 6 pm this evening to 6 am HST Friday for Maalaea Bay, Pailolo channel, Big Island southeast waters.