Photo Credit: Jason Weingardt

West Kaua’i

Today: Partly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 84 near the shore to around 71 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 near the shore to around 55 above 3000 feet. East winds up to 25 mph. Chance of rain 50 percent.

Tuesday: Breezy. Mostly cloudy with scattered showers. Highs around 84 near the shore to around 73 above 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 78 to 84. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 70. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Tuesday: Breezy. Mostly cloudy with numerous showers. Highs 76 to 81. East winds 15 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with numerous showers. Highs 71 to 77 in the valleys to around 63 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with occasional showers. Lows 63 to 68 in the valleys to around 51 above 4000 feet. East winds 10 to 25 mph. Chance of rain 90 percent.

Tuesday: Breezy. Mostly cloudy with occasional showers. Highs 73 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 25 mph. Chance of rain 90 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 72 to 83. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows 58 to 70. East winds up to 15 mph. Chance of rain 80 percent.

Tuesday: Mostly cloudy. Breezy. Numerous showers in the morning, then occasional showers in the afternoon. Highs 75 to 85. East winds 10 to 20 mph. Chance of rain 80 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 82. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows 62 to 70. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Breezy. Mostly cloudy with numerous showers. Highs 72 to 81. East winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate trade winds will strengthen to strong levels by Wednesday and persist through the week. A wet trade shower pattern will persist through much of the week with clouds and showers favoring windward areas with a few showers spilling over to leeward areas, especially as the winds strengthen.

Discussion

A weakening 1030 mb high lingers far northeast of the state while a front drapes across the middle of the Pacific 400 miles northwest of Kauai. A stronger 1038 mb high continues to develop behind the front and is producing near gale force winds just behind the front. A ridge extending from the high to northeast continues to produce moderate trades over the state. A band of low clouds and scattered light to a few moderate showers are streaming in along with the trade wind flow. These showers produced modest rainfall totals along windward areas overnight and is expected to continue through much of the day today as this band trains over the state. Following behind this band is a more expansive stratocumulus deck that should keep scattered low clouds and showers in the forecast through Tuesday.
The main focus of the forecast will stay on the developing strong winds. Models have been consistent in the anomalous strong high building north of the state by Wednesday. The front northwest of the state is expected to weaken to a surface trough during this time with a possible low developing. This will help to keep the gradient from getting too strong. However wind speeds will still strengthen around the state beginning as early as tonight that may require a wind advisory or even a high wind warning for some of the windier zones and persist through the week. The wind forecast still hedges on where and when this surface low and trough will develop with respect to the state. Thus, we will continue to monitor observations and latest model guidance to determine exact timing and extent of the wind hazards.
In the upper levels an elongated trough deepening just northwest of the state will cool temperatures and help destabilize the tradewind inversion. Temperatures along the upper slopes could drop near to below freezing and with a raised inversion height a slight chance of freezing rain on the upper slopes of the Big Island summit zones remains for tonight into Tuesday.
Wet trade showers are expected through the week. By late Tuesday into Wednesday, several impulses rotating through the upper level trough will lead to a mid- level cutoff low, initiating surface cyclogenesis along the stalled trough, about 550 miles northwest of Kauai Tuesday night into Wednesday. If the upper level low develops close enough to the state, locally heavy showers could develop, especially for the western end of the state Wednesday. This surface low is then expect to move far west of the state and dissipate.
Winds will ease slightly Thursday and Friday as the anomalously strong high pressure weakens. The upper level disturbance will persist very near or over the state that could help to keep active trade wind showers into the weekend.

Aviation

A weakening cold front will approach and stall northwest of the islands this week as a strong high pressure system slowly builds in across the Central Pacific basin. Easterly trade winds will strengthen over the next few days, blowing up into the breezy to locally windy range. A band of clouds, the remnants of an old frontal band, will drift into the islands from the north through today with increasing shower trends and brief MVFR conditions over all islands favoring windward airfields.
AIRMET Sierra for mountain obscurations remains in effect this morning for north through east sections from the island of Molokai to the Big Island as this band of low clouds runs up over the mountains.
AIRMET Tango for moderate low level turbulence over and southwest through northwest of mountains will also be needed later this morning.

Marine

High pressure far northwest of the coastal waters will track east and strengthen to near ~1052 mb as it passes north of the islands Tuesday and Wednesday. A surface trough is expected to develop between the coastal waters and the strong high pressure. The high will linger well north of the islands as it gradually weakens Thursday and Friday. Easterly trade winds will gradually strengthen over the next couple of days, approaching gale-force speeds in the channels when speeds peak around midweek. A Small Craft Advisory (SCA) has been issued for the typical windier waters around Maui County and the Big Island through tonight as winds increase today. The SCA will likely be expanded to all zones as winds and seas increase Tuesday and Wednesday. Guidance trends will be monitored to determine the need for a Gale Watch for the windier zones.
The small, short to medium period northwest swell will linger through Tuesday. A developing fetch of north winds to the north and northwest of the islands will generate a moderate (~6 feet) short- period (10-12 seconds) north swell that will build Tuesday and peak Wednesday before diminishing.
With the onset of strong trade winds, rough choppy wind waves are expected to increase through the week with a peak from Wednesday through Friday. It is likely east facing shores will exceed High Surf Advisory (HSA) criteria during the second half of the week. South facing shores will remain tiny through the week. An anomalously strong low pressure in the distant southeast Pacific has an associated fetch that may deliver a small, medium- period south- southeast swell by the end of the week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov