Hawaii Weather Synopsis: High pressure far north of the state continues to drive moderate trade winds across local waters. Passing low clouds and showers will favor windward and mauka areas through tonight with some high clouds lingering across the entire area. An upper low moving south will destabilize the airmass enough to trigger locally heavy showers and possibly thunderstorms, especially around the Big Island late tonight through Saturday night.
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 28 Oct 2011 at 9:30am HST
Trades will continue today across the state at generally moderate speeds. They will increase somewhat tonight and Saturday as the ridge far north of the area consolidates (see latest weather map), but may weaken again Sunday and Monday as a surface trough develops several hundred miles east of the state. This trough is expected to develop at the surface in response to upper level troughing which is presently sagging southward cutoff from the westerlies. There is some cold air aloft and jet energy associated with this upper trough and as this trough sags southward expect the airmass over the state to destabilize late today through Saturday night. As the coldest air and best upper level support for deep convection will be centered east of the Big Island, the details are tricky regarding how intense the shower activity will be during the next 48 hours.
Model to model agreement is good for the next 48 hours, but even a slight deviation will result in drastically different weather depending where one is in the state. At a minimum, it appears the trades will become wetter for all areas with more frequent and more intense showers late today through Saturday night. Terrain anchored showers will bring the highest threat for heavy rainfall in areas such as the Kona side of the Big Island and other leeward areas of the smaller islands. In addition, the lifted index becomes more negative, -2 to -3, as the cold pool mid levels and aloft slides by and a threat of thunderstorms exists for the windward coastal waters from Maui eastward and for the Big Island on Saturday and Saturday night. With the cooling aloft, but not super cold, any showers that develop Saturday and Saturday night over the Big Island summits will bring accumulating snowfall down to near 12000 feet. As confidence increases as to the timing of showers on the summits, NWS will need to consider a winter weather highlight. The weather is expected to generally improve Sunday afternoon as the airmass stabilizes and dries somewhat.
The pattern next week features an increasingly moist trade wind pattern as the remains of the weak surface trough to the east of the state drifts back westward across the state around midweek when lingering instability from a weakened trough aloft may allow for appreciable windward rainfall totals next week.
In the marine environment, a moderate size northwest swell is expected to build in Sunday night and Monday, peak Monday night near 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 Friday morning:
09 Princeville, Kauai – SE
16 Bellows AFB, and Kahuku, Oahu – ENE
23 Molokai – NE
16 Kahoolawe – ESE
21 Kahului, Maui – NE
08 Lanai – NE
28 South Point, Big Island – ENE
Here are the 24-hour precipitation totals (inches) for each of the islands as of Friday morning:
0.54 Mt. Waialeale, Kauai
0.59 Oahu Forest NWR, Oahu
0.19 Puu Kukui, Maui
3.06 Kealakekua, 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 FRI OCT 28 2011
Surf along north facing shores will be 4 to 6 feet today, lowering to 3 to 5 feet Saturday.
Surf along west facing shores will be 2 to 4 feet today, lowering to 1 to 3 feet Saturday.
Surf along south facing shores will be 1 to 3 feet through Saturday.
Surf along east facing shores will be 3 to 5 feet through Saturday.
Outlook through Thursday Nov 3: The current small northwest swell will diminish through Sunday. Forerunners from a larger northwest swell will arrive Sunday night. This swell will build on Monday, causing surf heights to approach the high surf advisory threshold of 15 feet for north facing shores from late Monday through early Tuesday. This swell will gradually lower through Thursday.