textproduct: Honolulu

SYNOPSIS

Wet and windy weather will continue across the islands today, with conditions gradually improving tonight as winds ease up some and rainfall coverage and intensity diminishes. A more typical trade wind pattern will then follow Tuesday through late this week, although it will remain rather breezy.

DISCUSSION

Currently at the surface, a trough of low pressure is located a few hundred miles southwest of the state, while a 1036 mb high is centered well to the north of the islands. The gradient remains strong locally, with breezy to windy conditions affecting much of the state. The strongest winds continue to be over and downwind of the higher terrain, through valleys, and in other local acceleration areas, where frequent wind gusts of 40 to 50 mph have been occurring overnight. Infrared satellite imagery shows overcast conditions across the islands. Radar imagery shows widespread rain from Oahu eastward, with lesser shower coverage over Kauai. The heaviest rainfall continues to focus over the windward portions of the islands. The main short term focus continues to revolve around the heavy rain and damaging wind potential today.

The overall forecast appears on track, with deep moisture remaining over the islands in association with the old dissipated front. This in combination with divergence aloft and strong winds aiding orographic lift, will continue to support areas of heavy rain primarily over windward slopes and coasts, along with a slight chance for a rumble or two of thunder. The Flood Watch remains in effect through 6 PM this evening.

The wind forecast is a bit more uncertain, as there has been a decrease in the gustiness overnight. We still expect a windy day across the islands however, as the gradient remains tight between a 1039 mb high well north of the state and a weak developing low several hundred miles southwest of the islands. As a result, the High Wind Warning remains in effect through 6 PM this evening as well.

Finally, the Winter Storm Warning for the Big Island summits remains in effect through 6 PM this evening for elevations above 12000 feet.

Conditions are expected to begin improving by late this afternoon, with winds easing up some, and rainfall diminishing in coverage and intensity as well. It will remain breezy enough tonight however, that a Wind Advisory may be needed for some of the typically windier areas once the High Wind Warning is cancelled.

More typical, but breezy, trade wind weather will follow Tuesday through Friday, with showers favoring windward and mauka areas. The latest 06Z GFS and 00Z ECMWF show the potential for another round of heavy rainfall next weekend. Since this has been a recent development in model trends showing a return of unsettled weather, will wait for some more run to run continuity before trending the forecast away from a trade wind pattern.

AVIATION

A broad, nearly stationary surface high prevails north of the Hawaiian Islands while an elongated upper-level trough meanders easterly will aid in generating strong to near gale force trades across the islands today. Additionally, scattered rain and lowered ceilings across the state will lead to MVFR and localized IFR conditions at times. Otherwise, gusty trades will be the primary impact throughout the period.

AIRMET Sierra is in effect for mtn obsc for all islands.

AIRMET Tango is in effect for mod to isol turb across all islands and adjacent waters due to the weather system over the state up to FL380. Sustained winds in excess of 30 kt is also expected into Monday.

Light icing is expected in cloud layer 120-FL250 across the state.

MARINE

A low pressure system southwest of the Hawaiian Islands slowly drifts westward as a strong high north of the state slowly drifts eastward. Wind speeds will weaken slightly through the day as both large scale pressure systems begin to move away from the island chain. Strong to gale force winds remain in the forecast today for both coastal and offshore waters, and a Gale Warning remains in effect through the afternoon hours for all Hawaiian waters. Fresh to locally strong easterly trade winds will linger in the forecast for all coastal waters with slight downward trends each day to Small Craft Advisory levels from Tuesday into Thursday.

These strong to gale force trade winds today will bring large and very rough surf along east facing shores lasting through tonight. A High Surf Warning remains in effect for exposed east facing shores through tonight. Surf heights along east facing shores will decline to advisory levels by Tuesday morning, then decline below advisory thresholds, yet remain rough from Tuesday night onward as trade winds ease across the region.

Small to moderate northwest swells will pass through the islands into the first half of next week. These smaller swells will keep surf heights on the smaller side. Looking into the extended forecast from the middle to the end of next week, we see a similar swell picture with no larger northwesterly swells for the foreseeable future.

Surf along south facing shores will remain small with some small background south swell energy expected over the next few days. Select southern exposures exposed to the wind swell will likely see some larger waves as well.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch through this afternoon for Niihau-Kauai Leeward- Kauai Mountains-Waianae Coast-Oahu North Shore-Olomana-Central Oahu-Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West- Maui Leeward West-Haleakala Summit-Kona-Kohala-Big Island Interior-Kauai North-Kauai East-Kauai South-East Honolulu- Honolulu Metro-Ewa Plain-Koolau Windward-Koolau Leeward-Molokai- Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley North-Maui Central Valley South-Windward Haleakala-Kipahulu- South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast-Big Island East-Big Island North.

High Wind Warning until 6 PM HST this evening for Niihau-Kauai Leeward-Kauai Mountains-Waianae Coast-Oahu North Shore-Olomana- Central Oahu-Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West-Maui Leeward West-Kohala-Big Island Interior-Kauai North-Kauai East-Kauai South-East Honolulu-Honolulu Metro-Ewa Plain-Koolau Windward-Koolau Leeward-Molokai-Lanai Windward- Lanai Leeward-Lanai South-Maui Central Valley North-Maui Central Valley South-Windward Haleakala-Kipahulu-South Maui/Upcountry- South Haleakala-Big Island South-Big Island Southeast-Big Island North.

High Surf Warning until 6 AM HST Tuesday for Olomana-Kahoolawe- Maui Windward West-Kauai East-East Honolulu-Koolau Windward- Molokai Windward-Molokai Southeast-Windward Haleakala-Kipahulu- South Haleakala-Big Island Southeast-Big Island East-Big Island North.

Winter Storm Warning until 6 PM HST this evening for Big Island Summits.

Gale Warning until 6 PM HST this evening for all Hawaiian waters-