Issued: Feb 09, 2010 8:30 PM HST
Synopsis
Moderate trade winds and dry conditions will prevail through early Wednesday. A weakening cold front will bring a few showers to Kauai and Oahu by late Wednesday as it dissipates. The trades will freshen from Thursday into Friday, and then diminish slightly into the weekend.
Discussion
Observations across the main Hawaiian islands reported light to moderate trade winds, and still virtually no rain. Aloft, ridging strengthened through a deep layer from the west, providing ample subsidence, as shown by the low inversion base in local soundings. Moisture content through the mixed layer approached the lower limit of what is possible for a tropical maritime air mass.
Dry trades will continue through tonight, when the next front will approach the state from the northwest. Although guidance predicts this feature to reach far enough south to brush the islands as it passes, the accompanying trough aloft will make only a small dent in the prevailing ridge. Without adequate support, the front near the surface likely will stall out even before reaching Kauai. Indeed, its main local effects may be limited to weakening the trades briefly before it arrives, and providing a little extra moisture for trade-wind showers from Wednesday into Thursday after it disintegrates.
The trade winds will increase somewhat from Wednesday into early Friday as the subtropical ridge recovers, but then will weaken again by late Friday ahead of the next front. Most solutions still portray this feature as being even less impressive than the one due earlier in the week, so dry trade winds likely will persist through the coming weekend, albeit at slightly lower speeds.
Guidance starts to disagree more by Monday. Some solutions wear away the ridge aloft over the islands, while others bring a stronger mid-level trough as a distinct feature. In any case, it looks like a front approaching the state early next week might have a little more support aloft, and so may actually produce a bit of rain.
Marine
A northwest swell generated by a large and intense storm system far northwest of the main Hawaiian islands will bring surf heights to warning levels from this evening through Thursday, before lowering to advisory levels on Friday. A reinforcing smaller northwest swell expected to come in on Saturday will maintain advisory-level surf into the weekend.
A south swell will arrive on Wednesday and peak late Wednesday night through Thursday morning along south-facing shores. The surf from this swell has the potential to reach the 8-foot high surf advisory threshold for south-facing shores.
Watches/Warnings/Advisories
High surf warning until 6 pm HST Thursday for Niihau, Kauai windward, Kauai leeward, Waianae coast, Oahu north shore, Oahu Koolau, Molokai, Maui windward west, Maui central valley, windward Haleakala, Kona, Kohala.
Small craft advisory until 6 pm HST Thursday for Kauai northwest waters, Kauai windward waters, Kauai leeward waters, Kauai channel, Oahu windward waters, Oahu leeward waters, Kaiwi Channel, Maui county windward waters, Maui county leeward waters, Alenuihaha channel, Big Island windward waters, Big Island leeward waters, Big Island southeast waters.