Hawaii Weather Synopsis: Gentle to moderate trade winds will focus clouds and showers over windward and mauka areas into Tuesday. Strengthening high pressure far north of the islands will produce increasing trade winds late Tuesday and Wednesday. The strengthening trade wind flow will carry an area of moisture over the islands, leading to an increase in showers and possibly unsettled weather. Gusty trade winds and somewhat unstable conditions are expected during the end of the work week.
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 31 Oct 2011 at 10:12am HST
Gentle to moderate trade winds will remain through Tuesday. Trade winds will be lightest today as a weak mid-level trough passes over the islands, leading to sea breezes over leeward sections of the smaller islands. A surface high pressure area currently far northeast of the islands (see latest weather map) will move east into the eastern north Pacific over the next couple of days, and another high from the west Pacific will move in to replace it. The pressure gradient over the state will increase in response, bringing an increase in trade winds Tuesday night.
Rainfall will be focused over mainly windward and mauka areas into Tuesday. A diffuse upper low remains east of Hilo and this low is forecast to slowly meander west over the next few days. The low is enhancing cloud tops over the coastal waters this morning with towering cumulus (TCU) east and SE of the Big Island and isolated TCU in Oahu’s coastal waters. Currently Hawaii sits just west of the upper low’s axis and temps aloft are expected to slowly drop over the next few days. This afternoon and Tuesday afternoon, the upper slopes of the leeward Big Island have the best chance of tapping into the instability aloft with a slight chance of thunderstorms. In addition, sea breezes may lead to an increase in showers over leeward sections of the smaller islands this afternoon.
Trade winds will increase late Tuesday into Wednesday. Strong high pressure will move far north of the islands Tuesday night then settle to the NNE during the second half of the week. Easterly trade winds will begin to build Tuesday night and will become locally breezy and gusty Wednesday and Thursday. The stronger trade winds will hold into next weekend.
An increase in showers is expected as trade winds strengthen Tuesday night and Wednesday, with unsettled weather possible as the upper low brings instability. An area of moisture currently east of the state will get carried westward in the building trade wind flow during this time. Currently, the forecast for thunderstorms is relegated to the slopes of the leeward Big Island, but this may be expanded depending on the strength of the upper low. Heavier showers may also be introduced to the forecast.
Uncertainty in the rainfall forecast increases toward the end of the work week and heading into next weekend. The GFS and ECMWF models show the above-mentioned upper low elongating and stalling in the vicinity of the state, but details remain unclear. The current forecast calls for a somewhat wet trade wind pattern, with confidence too low for any mention of thunderstorms.
No marine advisories are in effect. Winds should remain below the 25 kt Small Craft Advisory (SCA) threshold through Tuesday. As trades increase into Wednesday, SCA winds are likely for the typically windy waters around the Big Island and Maui. Little further change in winds is expected into next weekend.
Aside from a moderate northwest swell due today and Tuesday, mainly small swells are expected this week. Forerunners of the new northwest swell will build this morning, with north-shore surf peaking below the advisory level from this afternoon through Tuesday morning. Also, expect an increase in rough short-period surf along east-facing shores as trades build during midweek.
The following numbers represent the strongest wind gusts (mph), along with directions Monday morning:
12 Lihue, Kauai – ENE
14 Bellows AFB, Oahu – ENE
14 Kahoolawe – E
13 Lipoa, Maui – E, and Kahului Airport, Maui – NNE
18 South Point, Big Island – ENE
Here are the 24-hour precipitation totals (inches) for each of the islands as of Monday morning:
0.77 Mt. Waialeale, Kauai
2.06 Oahu Forest NWR, Oahu
0.18 Ulupalakua, Maui
0.33 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 MON OCT 31 2011
Surf along north facing shores will rise to 9 to 13 feet today, then lower to 8 to 12 feet on Tuesday.
Surf along west facing shores will rise to 5 to 8 feet today, then lower to 4 to 7 feet on Tuesday.
Surf along south facing shores will remain 1 to 3 feet through Tuesday morning, then rise to 2 to 4 feet by late Tuesday afternoon.
Surf along east facing shores will be 2 to 4 feet through Tuesday.
Outlook through Sunday Nov 6: The current northwest swell will gradually lower through the week with a new northwest swell expected to arrive toward the weekend. There will be a series of small south swells through the week with trade winds continuing to produce short period choppy surf along east facing shores.