textproduct: Honolulu

SYNOPSIS

Weak ridging will reside over the islands through Thanksgiving. The result will be a stable environment with mainly clear to partially cloudy skies and light winds. The lack of any significant trade flow, or just light southeast or variable breezes will make if feel more humid into the holiday weekend. Due to this wind pattern allowing the smaller islands to fall in the rain shadow of Big Island, any precipitation will be light and typically occur over further interior, leeward locales. Kauai and Niihau rainfall will likely increase early next week as a the tail end of a cold front approaching the area from the northwest stalls out near the Garden Isle.

DISCUSSION

A somewhat anemic high pressure ridge parked over the islands through the holiday weekend will produce just enough subsidence to maintain slightly above normal warmth, more humid days under partial cloudiness and light variable to southeasterly breezes. This afternoon's temperature inversion heights at both Lihue and Hilo are ranging between 5,000 to 6,000 feet. These stronger, relatively lower inversion heights are solid evidence of the subsidence as will be dry statewide conditions under fair weather cumulus. The position of the ridge in relation to the islands will also keep the state under a light southeasterly wind pattern. These light, synoptic scale winds under more sun and clear overnight skies will allow the local scale sea and land breezes to kick in over each island.

Southeasterly winds will produce a rain shadow effect as upstream air approaches the state and flows around Big Island. This equates to a disrupted (non-trade like) pattern and to lessened clouds as orographic lift over the island's topography will be limited. This will result in less frequent shower activity. We can't completely get away from the nature of the tropics so expect a few brief stray showers primarily along upslope higher terrain. The highest probabilities of precipitation will occur during the overnight to early morning hours over the eastern slopes of Big Island and Maui. Recent Kilauea volcanic activity from Episode 36 will increase the vog levels and the noticeable presence of haze through Thanksgiving.

The weather pattern changes early next week as a cold front approaches the state from the northwest. The forward motion of this boundary will slow and eventually stall near Kauai next Tuesday. Southerly winds ahead of the front pulling a more moisture-rich air mass over the western islands will likely increase mid to late week rainfall across Niihau, Kauai and Oahu. Wet weather will favor the southern and western slopes of Kauai and Oahu as the southerlies lift tropical moisture into the higher terrain. This may be the first significant weather maker of the wet season so it will be interesting to see how the forecast evolves through the holiday weekend.

AVIATION

Light east southeast winds tonight with gentle to moderate trades building across the eastern part of the state late Thursday. Sea breezes brought interior clouds this afternoon, which should begin to dissipate after sunset as land breezes fill in. Brief mountain obscurations may occur over the next few hours, but no AIRMETs in effect across Hawaii, or expected into Thursday.

MARINE

A surface ridge, parked just north of the state, will allow for mainly gentle to moderate east to east-southeast flow across the waters through the end of this week. However, winds are forecast to ramp up a bit for the typical windy areas around Maui and the Big Island Friday. Waters located in the lee of the islands will be more sheltered, and thus lighter flow with a nocturnally driven land/sea breeze pattern close to the coasts. Similar conditions will prevail through the weekend as a frontal system stalls north and west of the islands.

The current large long-period northwest swell will peak this evening then gradually decline over the next few days. A reinforcing northwest to north-northwest swell generated by a compact low passing north of the islands today should arrive Thursday night and could help maintain advisory level surf through parts of the day Friday. The current High Surf Advisory is in effect through early Friday morning for select north and west facing shores, but that may need to be extended depending on this reinforcing swell. With offshore buoy readings staying near or just below 10 feet with the current swell, we have held off on issuing a Small Craft Advisory (SCA) for our local waters exposed to the northwest swell.

Over the next few days, models rapidly deepen a low in the north Pacific, roughly 1,500 to 2,000 nm northwest of Kauai. A significant fetch of gale to storm force winds associated with this low will be pointed down the great circle route towards the island chain and will produce XL surf late this weekend. Wave Watch 3 (WW3) guidance seems to be roughly 6 hours earlier than the ECWAVE, but for the current forecast the timing has been adjusted towards EC solution due to a well known early bias of the WW3 model. Long-period forerunners should start arriving around mid-day Saturday, then quickly ramp up Saturday evening into the night. The peak of the event currently appears to be Saturday night into Sunday with the potential for giant surf (40 to 50 feet) along north facing shores Saturday night into Sunday out of the 300-320 degree swell direction. Surf heights will easily exceed High Surf Warning thresholds for select north and west facing shores, in addition to a SCA for rough seas.

Surf along east facing shores will remain small through the weekend due to the lighter winds. Select south facing shores could see some westerly wrap from the extra large northwest swell on Sunday.

FIRE WEATHER

While statewide precipitation will be on the down trend, lower wind speed and higher humidity will remain below critical fire weather thresholds through the weekend. Temperature inversion heights near Big Island and Maui will range between 5,000 to 6,000 feet.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Advisory until 4 AM HST Friday for Niihau-Kauai Leeward- Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North- Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.