A broad high pressure ridge north of the islands will produce moderate trade winds through Monday. Wind speeds will weaken from Tuesday through Thursday as a weak cold front passes north of the island chain. Trade winds slowly return by the end of next week, reaching moderate wind speeds by next Sunday, as the stalled front north of the islands diminishes and a broad ridge builds back into the region.
The infrared satellite imagery this morning continues to show a a shallow cold front roughly 400 miles northwest of Kauai approaching the Hawaii region. This frontal cloud band will weaken and stall out north of the state with no significant rainfall impacts. Closer to the islands unstable cumulus clouds streaming into the eastern half of the state producing periods of showers across the windward Hamakua and eastern slopes of the Big Island, including portions of East Maui. The most recent upper air weather balloon soundings from 2 AM HST (12Z) this morning show a significant difference between subsidence temperature inversion heights between Kauai at 5,500 feet and Hilo at 10,000 feet elevation level. This means less stable and taller clouds are moving into the eastern half of the state, enhancing shower activity. More stable clouds are capped around 6,000 feet elevation across the eastern islands producing only brief passing showers in the short term forecast.
Trade wind speed speeds will decrease as the frontal trough breaks down the ridge north of the island chain. Light large scale winds over Hawaii from Tuesday through Thursday will trigger and expansion of onshore sea breezes during the daylight hours and offshore land breezes overnight. These light local scale winds are driven by diurnal thermal differences between ocean temperatures and island heating/cooling cycles. Isolated showers are possible as sea breezes build clouds over island mountain and interior sections mainly during the afternoon hours. Rainfall amounts will be limited during this time period.
Trade winds gradually return as the frontal trough diminishes north of the islands and the ridge builds back into the region from Friday into the weekend. A hybrid trade wind sea breeze pattern will develop through Saturday, until moderate trade winds finally reassert themselves by next Sunday. Brief passing showers favor windward and mountain areas in the overnight to early morning hours.
Moderate to breezy easterly trades will persist, with clouds and brief showers favoring windward sites. Expect periods of MVFR conditions in showers, otherwise widespread VFR is expected.
AIRMET Sierra for mountain obscuration is now in effect for the windward sections of the Big Island and Maui. Conditions should improve later this morning.
No significant changes to the forecast this morning.
A cold front to the northwest of the islands continues to move to the east, disrupting a ridge to the north. Trade winds today will gradually weaken over the next couple of days as the ridge is eroded by the front. By midweek, winds are expected to be light and variable.
The current northwest swell (310-320 degrees) continues to be on the decline, and will continue to gradually fade tonight. Another small northwest swell is expected to arrive late tonight/early Monday morning, and will help to maintain elevated surf along north and west facing shores. A storm low near Japan is sending a long period northwest swell to the islands. This swell (320 degrees) is expected to arrive Thursday, surf is expected to peak below advisory levels.
The current south swell will hold today, and then gradually decline. As trades steadily weaken, wind waves and trade wind swell will follow with diminishing surf expected along east facing shores during the next several days.
None.
