textproduct: Honolulu

SYNOPSIS

A surface ridge will maintain light winds with land and sea breezes in place in most areas tonight through Thursday night. Isolated showers will affect mainly the coastal waters each night and the island interiors Thursday afternoon. A weakening front is forecast to increase showers late Thursday night across Kauai, with the showers spreading southeastward to the other islands Friday through Saturday. Another stronger front is forecast to bring breezy southwesterly winds late Sunday through Monday, with a band of heavier showers accompanying the front as it moves through the islands late Monday through Tuesday, followed by breezy northwesterly winds.

DISCUSSION

Currently at the surface, a 1028 mb high is centered to the distant northeast, with a ridge axis extending southwestward from the high to a location over the central islands. This is resulting in light winds with land breezes present or developing in most areas. Infrared satellite imagery shows daytime heating driven cloud cover decaying, with partly cloudy to mostly clear conditions in place across the state. Very dry conditions persist across the islands, with radar imagery showing very little if any shower activity. Rain gauges also have recorded no rainfall over the smaller islands in the past 6 hours, while a few gauges on the Big Island have measured 0.01 inches in the past 3 hours. The main short term focus revolves around an incoming front late Thursday and its impacts on the islands Friday into Saturday.

The ridge of high pressure over the central islands will shift slowly southeastward during the next day or so as a cold front approaches from the northwest. This will keep a light wind regime in place across the state, with land and sea breezes present in most areas. Shower activity should remain minimal and light, with most showers remaining offshore tonight and early Thursday. Some deeper moisture will move in ahead of the front Thursday afternoon, and this should result in a few more showers than what was seen today over the island interiors, but once again rainfall amounts should be minimal.

Model guidance remains in good agreement showing a cold front moving into Kauai through Kauai after midnight Thursday, then decaying as it shifts southeastward through Oahu and into Maui County on Friday, before stalling out and gradually dissipating in the vicinity of Maui and the Big Island Friday night and Saturday. The front will bring an increase in clouds and showers as it moves through, followed by a period of moderate to fresh north to northeast winds. The best forcing will remain well to the north of the state as the front moves through, so we don't anticipate any significant rainfall or flooding concerns with this feature.

The remnant moisture from the old front is expected to gradually lift back north of the islands Saturday night and Sunday, as yet another front approaches from the northwest. This front appears stronger, with moderate to breezy southwesterly winds developing in advance of the feature late Sunday through Monday. The front appears to move through the state late Monday through Tuesday, accompanied by a line of heavier showers with potentially gusty winds, followed by breezy northwesterly winds.

AVIATION

Light southeasterly background flow will give way to land and sea breezes pattern through the forecast period. This will provide the potential for low ceilings and interior clouds during the afternoon. VFR conditions are expected to prevail.

No AIRMETS are in effect.

MARINE

A weak ridge over the islands through Thursday will keep light and variable winds in the forecast with near shore sea breezes during the day and land breezes each night. A weak cold front moving in from the northwest on Friday will increase cloud cover and shower trends as it slowly drifts down the island chain through Saturday. Moderate to fresh northerly to northeasterly winds gradually filling in behind the front as it passes each island. Light and variable winds return to Hawaiian waters by Sunday, with southwesterly winds increasing ahead of the next cold frontal system approaching from the northwest. This next cold front moving into the islands from late Monday night into Tuesday appears stronger than the previous system, increasing chances for showers. Breezy northwesterly winds will build in behind the front as it passes.

Two significant northwest (310-320 degree) swells are expected to impact the state over the next several days, originating from a broad and complex low that evolved over the far northwest Pacific over the past few days. The first swell will begin building down the island chain on Thursday, an overlapping stronger long period northwest swell will build in on Friday. This will be a long duration event, with a peak centered around the Friday through Saturday time period. The swell will swiftly exceed warning levels from Friday through Saturday. This swell will then declines early next week before an even larger, extra large swell arrives in the islands by Tuesday.

Impacts associated with the warning-level surf Friday through Saturday will likely lead to minor water inundation over vulnerable low lying roadways and infrastructure. This likelihood will especially increase if the peak surf coincides with the overnight high tide cycle from Friday night to Saturday morning.

Surf along east-facing shores will remain small due to the lack of trades locally and upstream of the state.

Surf along south-facing shores will gradually decline Thursday as a small, long-period south-southwest swell gradually declines.

HFO WATCHES/WARNINGS/ADVISORIES

None.