FORECAST DISCUSSION

Synopsis

Very humid conditions with the chance for some enhanced showers will continue over the western islands tonight into early Thursday. Tropical moisture will then move west of the area by Thursday afternoon bringing some relief to the humid conditions as drier trade winds move in from the east. Breezy trade winds and much more comfortable conditions are then expected Friday through early next week, with showers focused over the windward slopes and mountains. The weather may get a bit more active by mid to late next week, as there is some indication that a tropical cyclone could approach the island chain from the east.

Discussion

Currently at the surface, a trough of low pressure is located around 500 miles to the west of Kauai, while a 1039 mb high is centered well to the north-northeast of the state. Infrared satellite imagery shows variably cloudy skies in place across the state. Meanwhile, radar imagery shows scattered showers across Oahu, with very little shower activity noted elsewhere. Main short term concern for tonight revolves around rain chances. Rest of tonight, The trough off to the west of the state will weaken and edge further westward, as deep layered ridging builds to the north of the island chain. This will allow trade winds to get established over the eastern islands by morning. MIMIC total precipitable water imagery shows a band of higher moisture between the Big Island and Oahu, with values between 2.0 and 2.2 inches, with some slightly drier air over Kauai and a notably drier airmass upstream of the Big Island. This band of higher moisture should shift slowly westward through the night, with Oahu and Kauai within the deepest tropical airmass through the overnight hours. As a result, some enhanced showers will be possible overnight across the western islands, with more of a trade wind shower pattern developing over eastern sections of the state. Thursday, Deep layer ridging will continue to build north of the area, allowing the trade winds to fill back in from east to west across the island chain. Trades should return to Oahu during the morning and to Kauai during the afternoon, bringing some relief to the oppressively humid conditions. The band of deeper moisture will remain over Oahu and Kauai during the morning, so some enhanced showers will remain possible. By afternoon however, the band of tropical moisture will begin to erode as it pushes further west, with a typical trade wind shower pattern overspreading the entire state. Thursday night through next Wednesday, High pressure to the north of the state will keep a moderate to locally breezy trade wind flow in place through early next week, with clouds and showers focused primarily over windward and mauka locales. Drier air will continue to move into the area on the east-northeasterly trades, with noticeably more comfortable humidity levels expected Friday through early next week. Attention then turns to the tropics, as both the 00z GFS and 00z ECMWF both show a pair of tropical cyclones moving westward toward the island chain by mid to late week. It's still way to early to tell what, if any, impacts could be seen here in Hawaii, but we will certainly be keeping a close eye these systems and the latest model trends.

Aviation

VFR will be the prevailing flying condition during the overnight hours with a strengthening pressure gradient and a drier and more stable air mass continuing to spread across the area from the east. Moderate trades will be in place by the end of Thursday. In the mean time, there are small, isolated pockets of instability still lingering around resulting in very isolated heavy showers with mainly MVFR conditions. No AIRMETs expected however.

Marine

High pressure will build well north of the state tonight, with moderate to locally fresh trades returning to eastern islands tonight, and into the western islands Thursday. As a result, small craft conditions are expected to develop over the windier waters around Maui and the Big Island Thursday, with winds remaining at advisory levels through at least Thursday night and likely continuing into the weekend. Short period trade wind swell will increase surf a notch along eastern facing shores Friday and into the weekend. Otherwise, no significant surf is expected.

HFO Watches/Warnings/Advisories

Small Craft Advisory from 6 AM Thursday to 6 AM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

Footer

DISCUSSION/MARINE...Jelsema AVIATION...Lau

Back to Top