Hawaii Island Weather Update for February 28th, 2020

Wet, Windy, and Unsettled conditions are expected this weekend and may persist through early next week. Gusty trade winds along with wet conditions and the possibility of thunderstorms are expected this weekend.


A few weather advisories are in effect for the island of Hawaii:


Wind Advisory has been issued 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 Watch has been issued for the summits of Maunakea and Mauna Loa through Sunday afternoon (March 1st). Snow and freezing rain are possible this weekend.


High Surf Advisory for the east facing shores for the island of Hawaii remains in effect until Sunday evening. Rough surf of 6 to 8 feet is expected through Saturday, later building to 8 to 12 feet on Sunday.

Synopsis


Wet and windy conditions will remain through the weekend. Strong trade winds will focus the majority of showers along windward slopes, but downpours will also occur over leeward locations. An upper low will bring a slight chance of thunderstorms and the possibility of winter weather to Haleakala and the Big Island summits through the weekend. Unsettled conditions may persist into early next week.

Discussion


A strong high pressure located far northeast of the state is expected to strengthen further over the next few days, boosting our already strong trade winds to near advisory levels. However, an upper level low now east of Hawaii will edge over the eastern portion of the state tonight and drift overhead this weekend, bringing increasing instability. This feature will likely weaken the local surface pressure gradient and keep the strongest trade winds to the northeast of the islands. Nonetheless, island winds are expected to be near advisory levels through the weekend before abating early next week as the high weakens. The aforementioned upper low will cool temperatures aloft and remove our normal stabilizing temperature inversion. Models have been consistently forecasting 500 mb temperatures near -16 C which is about as cold as it gets over Hawaii. These cold temperatures and associated instability will bring the chance for thunderstorms and locally heavy downpours. The strong winds near the surface will keep most of the heavy rain moving along at a fast pace, but windward areas will have a steady diet of moderate to heavy showers and isolated thunderstorms. The chances of flood advisories are likely, and a flash flood warning is not out of the question for windward areas, even with the strong trades. Highest rainfall totals are expected over the eastern half of the state as the coldest temperatures aloft and higher boundary layer moisture remains to the east. For leeward areas of the smaller islands, expect strong, gusty trade winds with quick hitting heavy showers. Winter weather at the higher elevations of the Big Island and Haleakala are a possibility as well. The upper low will drop freezing levels to 9000 feet or lower, so any moisture falling at the summits will be in the form of snow or freezing rain. The highest probability for winter weather on the summits appears to be on Saturday night into Sunday and a Winter Storm Watch has been issued for that time frame.

Aviation


A strong surface high located far northeast of the main Hawaiian Islands will maintain gusty northeast to east trade winds through Saturday. As a result, AIRMET TANGO remains in effect for moderate low-level turbulence below 090 immediately south through west of the mountains on all islands. The strong trades will also continue to transport low clouds with embedded showers into northeast facing sections of the islands this evening, producing brief periods of MVFR conditions due to lower ceilings and reduced visibilities. Otherwise, expect VFR conditions to prevail across most of the state. Low cloud and shower coverage will likely increase later tonight through Saturday due to the proximity of an upper level low, along with a slight chance of thunderstorms over the eastern half of the state. This could result in more widespread MVFR conditions over the higher terrain and northeast facing slopes and the need for AIRMET SIERRA for mountain obscuration over some islands. Strong winds on the west side of the aforementioned low could also result in an area of moderate upper-level turbulence tonight through Saturday. Will monitor the situation for possible issuance of AIRMET TANGO later tonight.

Marine


Strong high pressure northeast of the area is resulting in strong to near gale force winds across the coastal waters. A Small Craft Advisory (SCA) is in effect for all coastal waters through the weekend. At this time, it does not look like winds will reach gale force. An upper level low is expected to move over the state from the northeast tonight, introducing periods of locally heavy showers and a slight chance or thunderstorms through the weekend. The current northwest swell has peaked and the High Surf Advisory has been cancelled. This swell will then subside into the weekend, with no significant northwest swells expected into next week. Surf will also continue build along east facing shores as the trade winds strengthen. A High Surf Advisory is posted for east facing shores through the weekend. Surf may reach warning levels later this weekend into the beginning of next week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Sunday for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, South Big Island, Big Island North and East. Winter Storm Watch from Saturday evening through Sunday afternoon for Haleakala Summit, Big Island Summits. Small Craft Advisory until 6 PM HST Sunday for all Hawaiian waters.

WINTER STORM WATCH FOR BIG ISLAND AND HALEAKALA SUMMITS A cold core low sliding westward over the islands will bring cold temperatures on the highest elevations of the Big Island and Maui above 9,000 ft. Freezing rain and snow are possible. WINTER STORM WATCH IN EFFECT FROM SATURDAY EVENING THROUGH SUNDAY AFTERNOON * WHAT...Snow and freezing rain possible. * WHERE...Haleakala Summit and Big Island Summits. * WHEN...From Saturday evening through Sunday afternoon. * IMPACTS...Travel could be very difficult. Blowing snow will significantly reduce visibility at times, and ice will make roads treacherous. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Winter Storm Watch means there is potential for significant snow or ice accumulations that may impact the summits. Anyone planning travel to the summits, including hikers and campers, should monitor the latest forecasts and consider postponing their trip until improved weather returns.

HIGH SURF ADVISORY NOW IN EFFECT UNTIL 6 PM HST SUNDAY * WHAT...rough surf of 6 to 8 feet, building to 8 to 12 feet late Saturday into Sunday. * WHERE...east facing shores of Maui, Molokai, Oahu, and Kauai. * WHEN...Until 6 PM HST Sunday. * IMPACTS...Moderate. Strong breaking waves and strong currents will make swimming dangerous. PRECAUTIONARY/PREPAREDNESS ACTIONS Heed all advice from ocean safety officials and exercise caution. Stay away from the shoreline along the affected coasts.

WIND ADVISORY IN EFFECT UNTIL 6 AM HST MONDAY * WHAT...Northeast winds 20 to 35 mph with localized gusts over 45 mph. * WHERE...Portions of Lanai, Maui and the Big Island Hawaii. * WHEN...Until 6 AM HST Monday. * IMPACTS...Winds this strong are capable of downing tents or other temporary structures, as well as downing trees and causing power outages. PRECAUTIONARY/PREPAREDNESS ACTIONS... Motorists, especially those in high profile vehicles, are urged to drive with extreme caution. Motorists should use extra caution.

6 views
  • HIRSC Twitter