Hawaii Weather Synopsis: High pressure far northeast of the state places the islands in a light to locally moderate trade wind flow. Low clouds and light passing showers will favor windward and mauka areas through tonight with some high clouds present across the entire area. An upper low will dig down to a position near the state on Friday and linger into next week. This will cause instability with an increased chance of showers over portions of the state.
No Advisories, Watches, or Warnings are currently in effect.
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Broad Overview of Hawaii’s Weather
Based on the NWS Area Forecast Discussion for Hawaii, issued 27 Oct 2011 at 10:00am HST
Surface analyses show a 1025 mb surface high about 1650 miles northeast of the islands near 37°N 134°W with a ridge extending to a point about 350 miles north of Kauai, and a north to south surface trough about 900 miles west of Kauai along 175°W (see latest weather map). This pattern continues to produce moderate to locally fresh easterly trade winds over most areas of the main Hawaiian islands with lighter east-southeast flow near Oahu and Kauai. The global models show the trough west of Kauai moving west and weakening, while the high remains nearly stationary. These surface features will maintain gentle to locally fresh trade winds over the islands into the weekend.
Meanwhile, water vapor imagery and upper air analyses show a northeast to southwest ridge aloft over the islands. The ridge is forecast to remain over the area through Friday morning and keep the atmosphere relatively stable. The low level easterly flow will continue to produce showers over windward areas but the flow will be light enough to allow clouds and showers over interior and leeward areas in the afternoons. The ridge aloft will keep both windward and leeward showers generally light through Friday morning.
Global models remain in good agreement on a low aloft forming about 600 miles north of the islands this morning, then digging south toward the islands. On Saturday the low will become nearly stationary a few hundred miles northeast of the islands and linger there through early next week. The models show gentle to moderate trade winds continuing at the surface but colder temperatures aloft associated with the low will make the atmosphere less stable. This instability will allow clouds to build higher and produce heavier rainfall. The cold temperatures aloft also mean that frozen precipitation is possible over the Big Island summits as early as tomorrow evening.
The low aloft will gradually weaken and may open up into a trough but the trough may keep the atmosphere unstable, and the weather unsettled, through much of next week. However, the GFS and ECMWF models show much greater differences starting around the middle of next week and are therefore reducing NWS confidence in the forecast that far out.
In the marine environment, winds and seas will remain below small craft advisory levels through the weekend and on into next week.
A moderate size northwest swell is expected to build in Sunday night and Monday, peak Monday night just below advisory levels, then slowly lower into the middle of the week. There will also be a series of small southerly swells through the forecast period with trade winds continuing to produce short-period choppy surf along east facing shores.
The following numbers represent the strongest wind gusts (mph), along with directions late Thursday morning:
10 Princeville, Kauai – ENE
20 Honolulu Airport, Oahu – E
20 Molokai – NNE
22 Kahoolawe – E
22 Kahului, Maui – NE
07 Lanai – W
27 Upolu Airport, Big Island – ENE
Here are the 24-hour precipitation totals (inches) for each of the islands as of late Thursday morning:
0.53 Mt. Waialeale, Kauai
0.12 Manoa Lyon Arboretum, Oahu
0.08 Puu Kukui, Maui
0.36 Piihonua, Big Island
Here is the latest NWS rainfall forecast
Here are the latest available satellite images:
SURF ZONE FORECAST – OAHU
NATIONAL WEATHER SERVICE HONOLULU HI
900 AM HST THU OCT 27 2011
Surf along north facing shores will be 1 to 3 feet today, building to 4 to 6 feet Friday.
Surf along west facing shores will be 1 to 2 feet today, building to 2 to 4 feet Friday.
Surf along south facing shores will be 1 to 3 feet through Friday.
Surf along east facing shores will be 1 to 3 feet today, building to 3 to 5 feet Friday.
Outlook through Wednesday Nov 2: The small northwest swell on Friday will slowly diminish through Sunday. Forerunners from a larger northwest swell will arrive Sunday night. This swell will build on Monday, bringing surf to near the advisory level of 15 feet for north facing shores from late Monday through early Tuesday. This swell will lower through Wednesday.