Hawaii Weather Synopsis: An upper low over the state will continue the threat of heavy rainfall and thunderstorms through the weekend. With trade winds at low levels, rainfall will favor windward and mauka areas. Leeward areas will see showers as well especially during periods of stronger trade winds. A wet trade wind pattern will continue into next week.
Flash flood watch is in effect until 6 pm HST today for all main Hawaiian islands.
Winter Weather Advisory is in effect until 6 pm HST today for the Big Island summits.
A Small Craft Advisory is in effect until 6 pm HST Saturday for Maalaea Bay, Pailolo channel, Alenuihaha channel, Big Island leeward waters, Big Island southeast waters.
Click on the following link for the latest National Weather Service advisories and warnings: Wind/Surf/Flood related advisories or warnings
Broad Overview of Hawaii’s Weather
Based on the NWS Area Forecast Discussion for Hawaii, issued 4 Nov 2011 at 1000am HST
The National Weather Service has issued a flash flood watch for all Hawaiian islands. An unstable air mass coupled with an area of deep moisture has increased the threat of flash flooding. Early this morning eastern parts of Maui and the Big Island received heavy showers; a Flash Flood Warning for Maui expired at 7:15am. A Flash Flood Watch remains in effect for the entire state until this evening.
An upper low over the state will continue the threat of heavy rainfall and thunderstorms through the weekend. With trade winds at low levels, rainfall will favor windward and mauka areas. Leeward areas will see showers as well especially during periods of stronger trade winds. A wet trade wind pattern will continue into next week.
Local observations and spotters have reported strong winds picking up this morning as well, with some reports of gusts around 40 mph. Radar base velocity imagery from Molokai and Kauai showed a steady increase in winds.
Currently the Big Island summits are mostly clear. However, with the moist and unstable airmass, the likelihood for afternoon convection remains high, especially given the amount of insolation/heating on the Big Island. If convection develops across the Big Island slopes, it will likely reach the summit. Temperatures are currently below freezing at the summit, and are not expected to rebound much during the day. Any precipitation that reaches the summit will likely fall as snow, and a winter weather advisory remains in effect through the afternoon.
Marine forecast shows a strong high pressure remaining nearly stationary far northeast of the state. The pressure gradient across the islands is expected to be strong enough to maintain small craft advisory conditions of 25 knots through the typically windier channels near Maui and the Big Island. Seas are expected to be borderline just below the advisory level of 10 feet, which may bear watching for windward coastal waters.
Previous discussion issued at 9:40 am HST Thursday morning, Nov 3:
Breezy trade winds hold below 15,000 ft while the upper low over the state continues to support the threat for heavy rain, possibly through Saturday. Best chances for heavy rains and thunderstorms this morning is in the vicinity of the Big Island where the upper level cold pool is in phase with the most abundant boundary layer moisture. Another round of afternoon diurnally forced convection is likely along the leeward Big Island slopes this afternoon and Friday. Thunderstorm chances will shift west through tomorrow as the upper low absorbs an incoming short wave expanding the cold pool westward. The Winter Weather Advisory continues through 6 am HST Friday and will likely be extended. Elsewhere the most consistent rainfall will be focused on windward terrain.
The upper low will fluctuate in intensity over the next several days and continue to influence island weather. There will be some relief over the weekend as the deepest boundary layer moisture shifts west. However, with a mean weakness aloft and fairly consistent cold mid-level temperatures and persistent anticyclone to the north, a wet trade pattern will likely continue. Bouts of moderate to heavy rain may still occur in the longer term as frontal remnants and pockets of tropical moisture clip the area Sunday through Wednesday.
The following numbers represent the strongest wind gusts (mph), along with directions Friday morning:
27 Lihue, Kauai – ENE
24 Honolulu Airport, Oahu – NE
36 Molokai – NE
27 Kahoolawe – ENE
32 Kapalua-West Maui, Maui- NE
24 Lanai – NE
36 South Point, Big Island – ENE
Here are the 24-hour precipitation totals (inches) for each of the islands as of Friday morning:
2.11 Mt. Waialeale, Kauai
2.53 Oahu Forest NWR, Oahu
1.33 Puu Kukui, Maui
2.97 Pahoa, 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 NOV 4, 2011
Surf along north facing shores will be 2 to 5 feet today, increasing overnight to 6 to 9 feet by Saturday.
Surf along south facing shores will be 2 to 4 feet this morning, increasing to 3 to 6 feet late this afternoon through most of Saturday.
Surf along west facing shores will be 1 to 3 feet today and 3 to 5 feet tonight through most of Saturday.
Surf along east facing shores will be 3 to 5 feet through Saturday.
Outlook through Thursday Nov 10: A small to moderate northwest swell arriving today will peak late Saturday afternoon, then slowly subside into Monday. A small northwest swell arriving Tuesday night will peak Wednesday and diminish Thursday. A slight south swell will appear early this evening and subside late Saturday afternoon.