Daily Weather

Oct 21, 2014 4:00 AM HST

Synopsis
Synoptic southeast winds will prevail across the state in the next couple of days as a weak surface high pressure settles over the islands. A band of moisture associated with an old front northeast of the state will bring an increase in rainfall tonight and Wednesday. The stronger and more easterly trade winds will return later this week as a stronger high pressure moves to far north of the islands.

Discussion
Winds have shifted southeasterly over the eastern islands early this morning, and become lighter due to the shadowing effect of the islands. This allowed nighttime land breezes to develop, as indicated at Kahului airport observations. Rather moderate easterly winds are still over Kauai at this time, though as the day progresses, expect the synoptic southeasterly winds to spread. Early morning Lihue and Hilo soundings continue to reveal a trade wind weather type profile, with low level moisture extending to over 5 thousand feet. The soundings indicated a little drier, though still unstable air mass in the island vicinity. Latest satellite and radar data showed a little increase of low clouds in the island vicinity early this morning. As such, the islands will see a little more clouds and showers though rest of the morning. At 2 am HST, tropical storm Ana was located about 400 miles west of Lihue, and was moving to the west at 9 mph. Only high clouds from the convection associated the system are still affecting the state early this morning, especially over the western islands. The clearing of the high clouds over the state will be slow through the next couple of days.

A weak surface ridge of high pressure over the state is responsible for the southeasterly winds. This ridge will stay near the islands through the next couple of days. A dissipating front remains just north to northeast of the islands early this morning. Moisture from this dissipating front will spread south slowly and eventually reach the state by later tonight. Forecast models indicate air mass will still be somewhat unstable, though there is no prominent upper level feature providing more favorable atmospheric conditions for widespread heavy rain to develop. Therefore, expect an increase in low clouds and showers later tonight through Wednesday for the islands. Light winds across the state in the next couple of days will allow land and sea breezes to develop, and the converging day time sea breezes over the islands may result in more clouds and showers over the interior and lee areas.

A stronger surface high pressure is expected to move to far northeast of the state towards the weekend. Forecast models indicate areas of moisture will be passing the islands at times. Therefore, expect slightly more robust trade winds to return the state with periods of passing showers affecting mainly windward areas over the weekend.

Aviation
A deck of high clouds over portions of Oahu and Kauai will continue to thin today. Otherwise, 12Z soundings from PHLI and PHTO show the return of a low level inversion between 5 and 6 kft. Generally light winds will veer more SE today and interior areas may see afternoon cloud build ups. Terminals should remain predominately VFR through the afternoon. A sagging dissipating front is expected to bring enhance moisture to the state starting tonight, introducing the higher potential for periods of MVFR conditions.

Marine
Latest readings from the near-shore buoy north of Oahu still show the downward trend of the north-northwest swell. Believe surf for the north facing shores has decreased to below advisory level early this morning. Therefore the high surf advisory for north facing shores has been cancelled. A new small northwest swell is expected to arrive Thursday and continue through Friday, bringing below advisory level surf.

No small craft wind conditions are expected for the coastal waters through the rest of the week, as the winds are expected to remain below small craft advisory level, even for the usual windier coastal waters around Maui and the Big Island.

Watches/Warnings/Advisories
None.

All surf height observations and forecasts are for the full face surf height, from the trough to the crest of the wave.

Advisory and Warning Criteria
Location Advisory Warning
North-Facing Shores 15 Feet (8') 25 Feet
West-Facing Shores - Big Island 8 Feet (4'+) 12 Feet
West-Facing Shores - Remaining Islands 12 Feet (7') 20 Feet
South-Facing Shores 8 Feet (4'+) 15 Feet
East-Facing Shores 8 Feet (4'+) 15 Feet

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