Hawaii Weather Synopsis: Bouts of unsettled weather are in store this week. An upper level disturbance over the state will pose a threat for heavy showers, with thunderstorms possible over the Big Island and Maui today. With gentle to moderate trade winds blowing, showers will favor windward and mauka areas, though leeward areas will see their fair share of showers as well. Strengthening trade winds tonight and Wednesday will carry a moist air mass over the islands, bringing in wet trade wind weather through the weekend, while unstable conditions may lead to periods of locally heavy showers.
A Flash Flood Watch is in effect until 6 pm HST this evening for Kona, south Big Island, Big Island north and east, Kohala, and the Big Island interior.
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 1 Nov 2011 at 10:13am HST
Locally heavy rainfall remains a threat today for the state with thunderstorms possible over Maui and the Big Island. A Flash Flood Watch will continue through today over the Big Island with the most atmospheric instability over the orchid isle. Current radar, as of 9 am, shows thunderstorms over NE and SE coastal waters of the Big Island, and passing heavy showers over Molokai Oahu and Kauai, and the associated windward waters.
There are two main culprits for the increased rainfall and thunderstorms. The first, is an upper level low that has brought cold temperatures aloft over the state. The cold air has destabilized the atmosphere, removing our normal trade wind inversion that caps cloud growth. The second is enhanced moisture moving along with the trade winds increasing the chance of locally heavy rainfall. Overnight soundings showed an average precipitable water (PW) of 1.7 inches and satellite PW estimates agree showing above normal moisture upstream of the islands.
Wet conditions are expected today and into the weekend as the upstream moisture continues to ride in on strengthening trade winds. Trades will gradually strengthen as a strong surface high pressure sets up far north of the islands (see latest weather map). The stronger trades will focus clouds and showers over windward and mauka areas, while showers will periodically be blown over leeward sections of the smaller islands. The atmosphere will be somewhat unstable as the upper low continues to hover over the state, with locally heavy showers remaining a possibility.
In the marine environment, the current moderate northwest swell is peaking and will diminish today and Wednesday. Forerunners from another moderate northwest swell will arrive late Friday and fill in through the day on Saturday. A rough, short-period easterly trade swell will build by mid-week as the trade winds increase.
Winds should remain below the 25 kt Small Craft Advisory threshold today. As trades increase later tonight and Wednesday, small craft winds are expected for the typically windy waters around the Big Island and Maui. Also, as the trade swell builds by mid-week, seas may also approach the 10 ft threshold for a Small Craft Advisory.
The following numbers represent the strongest wind gusts (mph), along with directions late Tuesday morning:
15 Lihue, Kauai – ENE
18 Bellows AFB, Oahu – E
18 Kahoolawe – ESE
23 Kahului Airport, Maui – ENE
06 Lanai – WSW
20 South Point, Big Island – ENE
Here are the 24-hour precipitation totals (inches) for each of the islands as of late Tuesday morning:
1.67 Mt. Waialeale, Kauai
2.82 Oahu Forest NWR, Oahu
2.21 Mahinahina, Maui
2.73 Saddle Quarry, 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 TUE NOV 1, 2011
Surf along north facing shores will be 8 to 12 feet today then drop to 4 to 6 feet Wednesday.
Surf along west facing shores will be 4 to 7 today then drop to 2 to 4 feet Wednesday.
Surf along south facing shores will be 1 to 3 feet today then build to 2 to 4 feet this afternoon and hold through Wednesday.
Surf along east facing shores will remain 2 to 4 feet through Wednesday.
Outlook through Monday Nov 7: The current northwest swell will drop over the next couple of days. More northwest swell will build to double overhead this weekend. Minor amounts of southern hemisphere will persist this week. Choppy easterly trade swell will increase along windward reefs and beaches this week.