textproduct: Honolulu

SYNOPSIS

A surface ridge will maintain light winds with land and sea breezes in most areas through tonight. Isolated showers will affect mainly coastal areas this morning, with a few showers also developing over the island interiors this afternoon. A weakening front is forecast to increase showers late tonight across Kauai, with the showers spreading southeastward to the other islands Friday through Saturday, with moderate to fresh north to northeast winds building in behind the front. Another stronger front is forecast to approach later in the weekend, bringing breezy southwesterly winds late Sunday through Monday. A band of heavier showers is expected to accompany the front as it moves through the islands late Monday through Tuesday, followed by breezy northwesterly winds.

DISCUSSION

Currently at the surface, a 1027 mb high is centered to the distant northeast, with a ridge axis extending southwestward through the central islands. Meanwhile, a cold front is located about 150 miles northwest of Kauai. Light winds will prevail across the state today with afternoon sea breezes and overnight land breezes for most areas. Satellite imagery continues to show a band of clouds and showers over Oahu and portions of Maui County, with mostly clear to partly cloudy conditions over Kauai and the Big Island.

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. Some deeper moisture will move in ahead of the front this afternoon, and this should allow for the development of a few more showers than what was seen yesterday over the island interiors, but rainfall amounts should be minimal.

Model guidance remains in good agreement showing a cold front moving into Kauai after midnight tonight, 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

Pre-frontal convergence low clouds and scattered showers expected across Oahu and Maui County this morning. AIRMET Sierra is posted for tempo mountain obscurations above 3000 feet across the entire island of Oahu, with brief coverage across Maui County. Sea breezes will set in by afternoon and bring interior clouds for most areas through sunset. Additional AIRMET Sierra areas will be possible. Otherwise, expect VFR conditions for Kauai and Big Island through the rest of the morning.

An incoming weak front from the northwest will approach this evening and is expected to bring an increase in showers over Kauai late tonight and spread southeastward to the other islands by Friday. MVFR and lower ceilings are expected along the front over windward and northern terrain of Kauai and Oahu. North winds will build tonight along the front and veer northeast by Friday afternoon.

MARINE

A weak ridge over the islands today will produce light and variable winds with near shore sea breezes developing during the day and land breezes overnight. A weak cold front moving in from the northwest late tonight into Saturday will increase cloud cover and shower trends as it slowly drifts down the island chain. Moderate to fresh northerly to northeasterly winds will gradually fill in behind the front as it passes each island. Light and variable winds return to Hawaiian waters Saturday night and early Sunday, with moderate to locally strong southwesterly winds developing ahead of the next cold frontal system approaching from the northwest late Sunday through Monday. This next cold front will move down the island chain from late Monday night through Tuesday, increasing chances for showers. Fresh to locally strong northwesterly winds will build in behind the front as it passes.

Two significant northwest (300-320 degree) swells are expected to impact the state over the next several days. The first moderate to large long period northwest (300-320 degree) swell will build down the island chain today. Surf heights will build to High Surf Advisory levels along north and west facing shores of Niihau, Kauai and Oahu, thus a High Surf Advisory for these shores remains in effect through Friday afternoon. Seas will also rise above 10 feet, thus a Small Craft Advisory (SCA) around most Kauai and Oahu waters remains in effect. A slightly bigger, and longer period northwest (300-320 degree) swell will build in on Friday. This swell is expected to peak Friday afternoon and evening, pushing surf heights above warning levels through Saturday for select north and west facing shores. In addition the SCA will also expand to most coastal waters with this next swell. The large northwest swells will decline Saturday into early next week. A potentially extra large northwest (310-330 degree) swell may fill in from Tuesday onward next week.

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 as peak surf heights coincides with the overnight high tide cycle from Friday through Sunday.

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 today as a small, long-period south-southwest swell gradually declines.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Advisory until 6 PM HST Friday for Niihau-Kauai Leeward-Waianae Coast-Oahu North Shore-Kauai North.

Small Craft Advisory until 6 PM HST Friday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters.