Hawaii Island Weather Update for February 29th, 2020

Wet, Windy, and Unsettled conditions will continue throughout Hawaii Island through the weekend into early next week. Gusty trade winds along with moderate to heavy showers have been happening throughout East Hawaii and occasionally crossed over into West Hawaii districts.


A few weather advisories continue to remain in effect for the island of Hawaii:


Wind Advisory remains in effect for the island of Hawaii until Monday morning (March 2nd). Winds of 20 to 35 mph with stronger gust of 45 mph are possible through the weekend.


A Winter Storm Advisory has been issued for the summits of Maunakea and Mauna Loa through Sunday afternoon (March 1st). Snow and freezing rain are expected to continue through the weekend.


High Surf Advisory for the east-facing shores for the island of Hawaii remains in effect until Monday evening. Rough surf building to 8 to 12 feet is expected to occur through Sunday and slowly decline into the new week.

Report from: HIRSC Team - Hawaii Island Section/Weather Unit

info@hiradioscannercommunity.com


Synopsis


Windy and occasionally very wet trade wind weather will continue into Monday, with brief heavy downpours expected, and a slight chance of thunderstorms. Lighter winds and fewer showers are expected from Tuesday into Thursday, with both potentially increasing again heading into next weekend.

Discussion


Strong and gusty NE to E trade winds are being supported by a 1040 MB high centered far NNE of the islands. A potent mid-level low centered just E of the islands has destabilized the island atmosphere, thereby turning our typical trade wind showers into heavy downpours, with a few thunderstorms as well. Headlines currently include a Wind Advisory for all areas (except the summits, where criteria are higher) due to the strong trade winds gusting to 50 mph, especially in and near showers. Additionally, a Winter Weather Advisory for Maui and the Big Island summits and upper elevations remains posted, with freezing rain expected to be the primary impactful winter weather type, although some snow showers can't be ruled out with any heavy convective burst. Heavy showers are in the forecast through Sunday, but significant flooding is not expected as they are moving WSW at 30-40 mph, and won't remain over any one area for an extended period of time. Despite this rapid forward speed, a heavy downburst impressively dropped .28" of rain in 15 minutes this afternoon in Mililani. The latest visible satellite images show a relative minimal in clouds approaching the islands from the E, but radar continues to detect heavy rain cores transiting rapidly WSW, with island terrain enhancing the incoming moisture. Water vapor imagery highlights the circulation associated with the low aloft, with associated cold temperatures aloft thermodynamically destabilizing the atmosphere, leading to quite a few heavy showers, despite relatively low PWAT (near 1 inch) and surface dew points in the upper 50s to lower 60s. Afternoon soundings highlight the unstable island atmosphere, with the freezing level near 10000' noted at PHTO. Temperatures over the Big Island/Haleakala summits are about as cold as we typically observe, and this will continue tonight, with gradual warming thereafter, but still likely cold enough to support the potential for winter weather through Sunday night. The latest analysis indicates a subtle N-S gradient in trade wind speeds, with winds stronger over the N half of the area, as opposed to the S half. This is expected to continue over the next 48 hours or so, as a weak and subtle surface trough develops E/SE of the islands in response to the low aloft. Although the statewide Wind Advisory extends through Sunday night, there is higher confidence in it verifying over Kauai and Oahu where winds are expected to increase slightly as the trough develops. Peak wind speeds are expected from tonight through Sunday night, with winds diminishing thereafter (and veering to the SE) as the surface trough moves from E to W across the islands Monday and Tuesday. The slow-moving mid-level low is expected to linger near the islands through Sunday night before lifting out to the N Monday/Tuesday, with a zonal flow aloft expected. The lighter winds and warming temps aloft will lead to a much more settled weather pattern into Thursday, with fewer showers. Diminished trade winds will prevail until the end of the week as the nearby surface trough keeps the gradient relaxed. As the trough dissipates and a new strong high builds N islands Friday into the weekend, trade winds will likely increase. A weak upper-level trough could increase shower coverage, but not to the extent currently observed.


Aviation


High pressure to the north of the islands will help produce moderate to strong northeasterly trade winds through tonight. A low-pressure system approaching the islands from the northeast will bring an increase in shower activity to all islands, mainly affecting the windward portions, though a few showers could spill over the terrain and into leeward areas. In addition, isolated thunderstorms may occur due to the unstable air aloft associated with this feature. Periods of MVFR conditions will be present along the windward portions of the islands with isolated MVFR conditions on leeward portions due to mountain obscuration from low clouds and showers. AIRMET Sierra remains in effect for mountain obscuration across windward sections of Molokai, Maui, and the Big Island. These conditions should persist through the night. AIRMET Tango remains in effect for low-level turbulence over and downwind of the terrain of all islands. These conditions will likely persist through the weekend. AIRMET Tango also remains in effect for upper-level turbulence over Kauai and Oahu. These conditions will likely persist through the night.

Marine

Strong east-northeast trades associated with 1040 MB high-pressure northeast of the state will persist through Monday. Pailolo and Alenuihaha Channels, Maalaea Bay and waters around South Point of the Big Island will remain near gale-force levels through Sunday. WAVEWATCH III and ECMWF-Wave guidance depict seas building into the 12-18 ft range by tonight across much of the area within a couple of hundred nautical miles to the northeast of the windward waters. The Small Craft Advisory (SCA) remains in effect for all waters due to a combination of winds and seas through Monday. In addition to the rough water conditions, shower coverage will increase through the rest of the weekend, along with isolated thunderstorms, as an upper low moves into the area. A surface trough is forecast to move through the waters from east to west through early next week, possibly with a brief period when the local winds trend down into the light to moderate range for some locations (low confidence this far out). Surf along east facing shores will steadily rise through the weekend due to the aforementioned scenario evolving over and upstream of the islands. Heights will climb to near warning levels later tonight through Monday. Will monitor buoys for potential need for upgrade to High Surf Warning. Surf along north and west facing shores will gradually ease over the weekend as the northwest swell that peaked Friday eases. This will be the beginning a quiet stretch for north and west facing shores through much of next week. Some of the trade wind energy, however, may wrap into exposed north facing shores each day. Surf along south facing shores will remain small with mainly background south and south-southwest swells.

HFO Watches/Warnings/Advisories


Wind Advisory until 6 AM HST Monday for all areas except the summits of Haleakala and the Big Island. High Surf Advisory until 6 PM HST Monday for East facing shores of Kauai Oahu Molokai Maui and the Big Island. Winter Weather Advisory until 6 PM HST Sunday for Haleakala Summit and Big Island Summits. Small Craft Advisory until 6 PM HST Monday for all Hawaiian waters.

WINTER WEATHER ADVISORY FOR SUMMITS AND UPPER ELEVATIONS OF MAUI AND THE BIG ISLAND A low-pressure system over the islands is bringing very cold temperatures to the higher elevations of Maui and the Big Island, leading to wintry weather above 9000 feet. The main threat will be freezing rain leading to ice-covered roadways, especially at night and early morning, with some snow showers expected over the Big Island summits. WINTER WEATHER ADVISORY REMAINS IN EFFECT UNTIL 6 PM HST SUNDAY * WHAT...Freezing rain expected. Some snow expected on the Big Island summits. Additional snow accumulations of up to 3 inches. Winds gusting as high as 40 mph. * WHERE...Haleakala Summit and Big Island Summits. * WHEN...Until 6 PM HST Sunday. * IMPACTS...Travel could be very difficult, leading to road closures. Summit roadways will likely become dangerously slippery due to patches of ice mixed with areas of snow, with reduced visibility at times. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Winter Weather Advisory means that periods of snow, sleet, or freezing rain will cause travel difficulties. Postpone travel plans to the summits until weather conditions improve, as warmer and drier conditions are expected by Monday.

HIGH SURF ADVISORY REMAINS IN EFFECT UNTIL 6 PM HST MONDAY * WHAT...Surf will be 6 to 8 feet this evening, rising to 8 to 12 feet tonight and Sunday. * WHERE...East facing shores of Kauai, Oahu, Molokai, Maui and the Big Island. * WHEN...Until 6 PM HST Monday. * IMPACTS...Moderate. Strong breaking waves and currents will make entering the water dangerous. Several days with these conditions will likely lead to significant beach erosion in some areas.

WIND ADVISORY REMAINS IN EFFECT UNTIL 6 AM HST MONDAY * WHAT...Northeast to east winds 20 to 35 mph with gusts near 50 mph, especially in showers. * WHERE...All areas except the summits of Maui and the Big Island. * WHEN...Until 6 AM HST Monday. * IMPACTS...Winds this strong are capable of causing localized power outages, downing tents or other temporary structures, as well as breaking tree branches. PRECAUTIONARY/PREPAREDNESS ACTIONS... Motorists, especially those in high profile vehicles, are urged to drive with caution. Secure trash cans, lawn furniture, and other loose objects that can easily be blown around by strong wind gusts.

Maunakea Access Road Information Update for February 29th, 2020 @ 16:45 (4:45 pm):


Aloha, The Maunakea Access road is closed at the Visitor Information Center located at an elevation of 9,200 feet due to: Below freezing temperatures, high humidity, snow, and icy road conditions. The Maunakea Observatories Forecast has posted a weather warning for Fog, ice and flurries. A chance for convection. Thank you for your patience and understanding. This report will be updated when information becomes available.

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