Photo Credit: Brendan Stephen

West Kaua’i

Rest Of Today: Breezy. Mostly cloudy with isolated showers. Highs around 80 near the shore to around 68 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to around 58 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 80 near the shore to around 68 above 3000 feet. East winds up to 25 mph. Chance of rain 50 percent.

South Kaua’i

Rest Of Today: Breezy. Cloudy with scattered showers. Highs around 79. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Cloudy with scattered showers. Lows 65 to 70. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tuesday: Cloudy and breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Rest Of Today: Cloudy and breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 67 to 75 in the valleys to around 62 above 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy and breezy. Numerous showers in the evening, then showers after midnight. Lows 58 to 63 in the valleys to around 52 above 4000 feet. East winds up to 25 mph. Chance of rain 90 percent.

Tuesday: Cloudy and breezy. Showers in the morning, then numerous showers in the afternoon. Highs 67 to 75 in the valleys to around 62 above 4000 feet. East winds 10 to 25 mph. Chance of rain 80 percent.

North Kaua’i

Rest Of Today: Cloudy and breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 72 to 79. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Cloudy with scattered showers. Lows 61 to 70. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Mostly cloudy with scattered showers. Highs 72 to 79. East winds 10 to 25 mph. Chance of rain 50 percent.

East Kaua’i

Rest Of Today: Cloudy and breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 72 to 79. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 59 to 71. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Cloudy and breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 79. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

The high pressure ridge north of the islands will build through Wednesday, strengthening the trade wind speeds into the breezy to locally windy range by Tuesday and Wednesday. Showers remain in the forecast with the highest coverage expected during the overnight and early morning hours. Extensive high cirrus clouds will continue through much of this week due to a subtropical jet stream in the upper levels. Breezy trade winds continue through Friday, then a slight decrease in wind speeds is forecast through the weekend.

Discussion

The satellite imagery this morning continues to show a large band of cirrus clouds over the Hawaii region caused by a subtropical jet stream as shown by the transverse banding on the water vapor imagery. A narrow upper level trough (also known as the Tropical Upper Tropospheric Trough or T.U.T.T.) is shown north through west of the island chain. Divergence aloft within the subtropical jet stream will help to produce showers across the area through much of this week. Local radar imagery shows bands of showers drifting into each island on the trade winds this morning with some of the stronger showers spreading rainfall into typically drier leeward areas.
A strong high pressure system will build north of the Hawaiian Islands through the week, ramping up trade winds into the breezy to locally windy range mostly on Tuesday and Wednesday. A Wind Advisory may be needed on Tuesday and Wednesday for windier areas across the state. Wind speeds will remain at breezy levels from Thursday to Friday as another high center moves into the Central Pacific basin and merges with the existing high. This combined high pressure system will then drift eastward away from the state on Saturday and Sunday with decreasing trade wind trends to more moderate speeds just in time for the weekend.
The island weather pattern will remain fairly wet this week with passing showers day and night for all islands through at least Thursday. Windward and mountain areas will see higher rainfall amounts than the typically drier leeward areas. Shower coverage will also favor overnight to early morning hours. This enhanced shower activity is caused by the upper level divergence associated with the jet stream and the added divergence along the southeastern side of the upper trough. By Friday and Saturday the axis of this upper trough will drift over the islands, stronger subsidence (downward vertical motions) will develop under the upper trough axis and from an upper level ridge building in from the west. This added atmospheric stability over Hawaii will reduce shower coverage and produce a drier weather pattern for this upcoming weekend.

Aviation

Breezy trade winds will focus light showers along windward areas through the next 24 hours and then the trades will strengthen heading into Tuesday. Periods of MVFR conditions will be possible in these showers, mostly during the overnight to early morning hours when better shower coverage is expected. Otherwise, VFR conditions will prevail.
No AIRMETs are in effect. However, winds under the inversion may strengthen enough by later this morning to bring some moderate low level turbulence downstream of the island terrain, and an AIRMET Tango may be needed. With winds strengthening into Tuesday, AIRMET Tango looks more likely to be needed by tonight.

Marine

Surface high pressure far north of the Hawaiian Islands will remain nearly stationary through the middle of the week before weakening. Winds look to slowly ramp up today and remain near fresh to locally near gale force Tuesday and Wednesday. Winds look to slightly weaken Thursday into the end of the week. Rough seas are expected to continue over all Hawaiian waters due to a combination of strong trade winds, a mix of northeast wind waves and a large long-period northeast swell. Therefore, a Small Craft Advisory (SCA) for all coastal waters has been issued through Tuesday night. The SCA coverage area may need to be adjusted as the northeast swell declines Tuesday.
A large, long-period northeast swell from a broad gale centered around 1600 nm northeast of the state has generated warning level surf for east facing shores this morning. A High Surf Warning (HSW) has been issued for all east facing shores and a High Surf Advisory (HSA) has been issued for all north facing shores through the day. The HSW for east facing shores may be downgraded to a HSA tonight as the energy eases across the islands. Due to the direction and magnitude of the swell, impacts to low- lying coastal areas and roadways are expected today especially coinciding with the peak early morning high tide.
Areas exposed to the northeast swell on north facing shores will be in HSA criteria today before dropping off this evening. A small medium-period northwest swell arrives late tonight into Tuesday. Another larger northwest swell looks to build in near HSA levels along north facing shores Thursday to Friday. A small long period south swell will build into the region with a slight bump in south shore surf activity lasting into Tuesday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for north facing shores of Kauai, Oahu, Molokai, Maui and Big Island.
High Surf Warning until 6 PM HST this evening for east facing shores of Kauai, Oahu, Molokai, Maui and Big Island.
Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian waters,

Data Courtesy of NOAA.gov