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Nov
03
2011

Hawaii Weather Overview


Hawaii Weather Synopsis: Expect unstable weather across the main Hawaiian islands into the weekend with heavy rainfall and possible thunderstorms. Rainfall will favor windward and mauka areas. Leeward areas will see substantial rainfall as well. A wet trade wind pattern will continue next week.

A Winter Weather Advisory is in effect until 6 am HST Friday 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.

 

PDC Global Hazards Atlas showing the Hawaiian Islands with TRMM 3-hour precipitation accumulations.

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 3 Nov 2011 at 9:40am HST  

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.

Previous discussion issued at 400 am HST Thursday morning, Nov 3: 

Heavy showers shifted offshore overnight, but cold tops noted in satellite imagery shows thunderstorms continue to fire within local waters around Maui and the Big Island this morning. Clouds and showers dropped off most noticeably over and around Kauai and Oahu, prompting a few forecast changes through the morning. The lull is likely temporary. Satellite imagery shows an upper trough axis extends southwest to northeast just east of the main islands, with a short wave wrapping eastward through the base of the trough just south of the islands. This short wave tapped an area of low level moisture across the eastern islands beginning last evening and this feature remains the main driver for heavy showers east of Molokai. The overnight shift in heavy rainfall to offshore areas can likely be attributed to the Big Island bow wave triggering deep convection instead of daytime heating over the islands themselves. We expect heavy rainfall to shift back onshore as the day wears on. Also, models show the upper trough will deepen today as another short wave swings through. Mid-level cooling and steepening lapse rates will support the threat for heavy rain and thunderstorms through Friday, with these gradually tapering off into the weekend. Frozen precipitation is possible over the highest elevations of the Big Island and a winter weather advisory remains in effect there through early Friday morning.

High pressure north of the state is driving the easterly trade wind flow across local waters at low and mid levels. While the upper troughing hinders full trade strength, the pressure gradient remains steep enough across the islands to support advisory-strength easterly trades across waters around the Big Island. Models show trades will remain strong enough in this area to keep the Small Craft Advisory in effect through Saturday.

Models show trade winds will prevail next week and a wet trade wind pattern is expected through the forecast period.

In the marine environment, breezy trades will prevail across the coastal waters for the next several days. Expect 20 kt winds with seas 5-8 ft, except up to 25 kt winds and seas 10-11 ft in the channels around Maui and Hawaii counties. A Small Craft Advisory remains posted for these typically windier areas into the weekend and may be extended. Heavy showers and thunderstorms remain possible through tomorrow. They can produce reduced visibilities, lightning and brief highers seas.

Only modest surf is in the water around the state today. South facing beaches are pulling in some head high surf which will taper off slowly over the next few days. The north shore will not see significant surf until Saturday when top areas should reach double overhead with some larger sets then drop thereafter. Elsewhere the breezy trades will keep consistent short period chop breaking on windward beaches and reefs. The longer term for both north and south shores is looking well below average.

The following numbers represent the strongest wind gusts (mph), along with directions Thursday morning:

20                 Lihue, Kauai – ENE
25                 Honolulu Airport, Oahu – ENE
27                 Molokai – NE
31                 Kahoolawe – E
25                 Lipoa – E, and Kahului Airport – ENE, Maui
12                 Lanai – NE
36                 South Point, Big Island – ENE

Here are the 24-hour precipitation totals (inches) for each of the islands as of Thursday morning:

4.11              Mt. Waialeale, Kauai
0.88              Waiawa C. F., Oahu
0.40              Molokai
0.00              Lanai
0.00              Kahoolawe
1.78              Kaupo Gap, Maui
4.85              Piihonua, Big Island

Here is the latest NWS rainfall forecast

Here are the latest available satellite images:

Hawaii Infrared satellite image 
Animated Satellite image of Hawaii region
Latest satellite image – Close-in visible satellite view
Latest radar image – Looping

SURF ZONE FORECAST – OAHU
NATIONAL WEATHER SERVICE HONOLULU HI
900 AM HST THU NOV 3, 2011

Surf along north facing shores will be 1 to 3 feet today, building to 2 to 4 feet Friday.

Surf along south facing shores will be 2 to 4 feet through Friday.

Surf along west facing shores will be 1 to 3 feet through Friday.

Surf along east facing shores will be 3 to 5 feet through Friday.

Outlook through Wednesday Nov 9: A small to moderate northwest swell arriving Friday night will peak late Saturday, then gradually subside through Tuesday. A small northwest swell is expected during the middle of next week. The current south swell will fade this evening, and will be replaced by another small south swell for Friday and Saturday.

NOAA animated wave model