Dry and stable conditions will persist under moderate east-southeast flow through Thursday night. A front is expected to bring wetter conditions to the western end of the state Friday into the weekend. This front will also introduce a slight chance of thunderstorms to Kauai and surrounding waters Friday afternoon into Saturday.
There is little change in forecast philosophy from last evening. The main Hawaiian islands lie along the far southwest flank of high pressure centered near 33°N 138°W. While the ridge extending southwest from this high lies north of the islands, technically placing us within trade wind flow, a front to our northwest has deformed the wind field and east southeasterlies prevail across local waters. Overnight soundings show our airmass is slightly more moist than last evening, with about 1.2 inches of precipitable water, and neutrally stable. An inversion near 7800 feet is likely capping convection. We continue to see a hybrid trade wind/seabreeze weather pattern as the Big Island blocks most of the wind flow across leeward areas of the smaller islands, but east-southeast trade winds continue to reach windward areas.
Models show the current pattern will continue through the work week. Blocked flow caused by the Big Island will allow the development of land and sea breezes across leeward sections of the smaller islands. We expect daytime cloud build ups with scattered showers over the island interiors, then clearing at night. Windward and mauka areas will see partly to mostly cloudy skies with a few showers. Weak ridging aloft will keep the atmosphere relatively stable and any showers light.
A cold front will approach Kauai on Friday. This front should initially have good upper level support due to an intruding upper level low far to the northwest, before moving away to the north Saturday night. Models generally agree on the handling of this feature, bringing the front across Kauai Friday, stalling it through Sunday, then weakening it to a trough before kicking it back westward early next week. The 00Z ECMWF pushes the front closer to Oahu than the 06Z GFS before stalling it, but the general sensible weather picture remains similar. We expect weaker southeast winds statewide from Friday through the weekend. Local sea breezes will continue for leeward slopes. By late this week, Kauai should be significantly wetter than the other islands with the possibility for some heavier showers and thunderstorms late Friday into Saturday. Light east-southeast trades are then expected to build back in early next week as the frontal remnants retreat westward.