Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny. Isolated showers in the late morning and afternoon. Highs around 83 near the shore to around 69 above 3000 feet. Northwest winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 65 near the shore to around 54 above 3000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 81 near the shore to around 68 above 3000 feet. Southwest winds up to 10 mph. Chance of rain 60 percent.

South Kaua’i

Today: Mostly sunny. Highs around 82. West winds 10 to 15 mph decreasing to up to 15 mph in the afternoon.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 63. Light winds. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 82. East winds up to 10 mph shifting to the southwest around 10 mph in the afternoon. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly sunny. Scattered showers in the late morning and afternoon. Highs 74 to 80 in the valleys to around 64 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 56 to 62 in the valleys to around 52 above 4000 feet. Light winds. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 78 in the valleys to around 62 above 4000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny. Isolated showers in the late morning and afternoon. Highs 71 to 82. West winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 57 to 65. West winds up to 10 mph in the evening becoming light. Chance of rain 70 percent.

Tuesday: Partly sunny with scattered showers. Highs 70 to 80. Light winds. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny. Highs 74 to 83. Northwest winds up to 10 mph shifting to the east in the afternoon.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 56 to 67. Light winds. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 71 to 81. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A low pressure system passing north of the Hawaii region over the next two days will keep light winds with day time sea breezes in the forecast through Tuesday. Isolated shower activity will increase over Kauai and Oahu by this evening as convergence bands moves into the western islands, with enhanced showers spreading into Maui County by Wednesday morning. A cold front will sweep from west to east down the island chain from Wednesday night through Friday. A band of clouds and showers will march down the island chain with this next system. Cool, moderate to breezy north to northeast winds will rapidly fill in behind the front affecting all islands from Thursday morning onward.

Discussion

This mornings satellite imagery shows only a few rain producing cloud bands over the eastern Big Island this morning. Otherwise conditions appear more stable due, in part, to the offshore land breezes. More stable conditions appear to be limiting showers over the western islands this morning as subsidence inversion heights were measured around 5,500 feet by the 2 AM HST upper air balloon sounding at Lihue. While less stable conditions are observed near the Big Island where subsidence inversion heights were measured around 6,500 feet by the 2 AM HST upper air balloon sounding at Hilo. Two cloud bands northwest of Kauai show our next opportunities for enhanced shower activity. These first two weak cloud bands will increase showers across the western islands later this evening through Tuesday. The second much larger cloud band, currently near the International Date Line, is associated with a eastward moving cold front that will sweep into the western islands from Wednesday night to Thursday morning.
Stronger winds aloft will keep a High Wind Warning in effect for the Big Island summits of Mauna Kea and Mauna Loa through early Tuesday morning. Surface wind observations this morning at the summit level are reporting sustained wind speeds in the 50 to 70 MPH range with gusts near 80 mph.
Elsewhere, light winds will continue for all islands with increasing shower trends for the western islands are forecast tonight through Tuesday. This first round of increasing showers are related to two convergence boundaries associated with a weakening cold front. Light large scale winds will allow local scale land and sea breeze winds to develop over each island. Day time sea breezes will build clouds over island mountain and interior sections each day with night time land breezes clearing out clouds over most islands.
The next cold front will sweep from west to east across the Hawaiian islands from Wednesday night through Friday. Expect increasing clouds and showers along this frontal band. A twelve hour period of wet weather will affect all islands as the frontal band passes quickly through the region. Scattered showers will linger along north slopes of each island after the frontal passage.
High pressure will rapidly build in behind the front, producing cooler temperatures along with moderate to breezy north to northeast winds. Model guidance remains in good agreement with this high confidence solution. Moderate to breezy trade winds with passing windward and mountain showers will continue through this weekend as a fairly strong high pressure system passes by just north of the Hawaiian Islands from Saturday to Sunday.

Aviation

Light background flow will once again allow for land breezes early this morning followed by sea breeze development this afternoon. Sea breeze convergence and differential heating may help generate showers over the interior by the afternoon, but not expecting anything widespread. VFR conditions and mainly sunny elsewhere.
No AIRMETs are in effect and none are expected during the forecast period.

Marine

Light and variable winds will hold through Tuesday, then shift out of the southwest and increase late Tuesday night through Wednesday as a front approaches. Guidance remains persistent and shows this front moving through Wednesday night through Thursday, with a ridge nosing eastward in its wake Thursday through Friday. The surface winds will quickly shift from southwest to northerly as the front moves through Wednesday night. These northerly winds may reach the moderate to fresh range Thursday through Friday as they gradually veer out of the northeast.
Surf along north and west facing shores will remain small through midweek, with mainly background, short- to medium-period northwest swell moving through. Although there are some minor differences between the ECMWF-Wave and GFSWave model guidance, both depict a significant northwest (320 degrees) swell arriving late Wednesday night, then rapidly building down the island chain through the day Thursday. This swell will peak late Thursday into Thursday night, then slowly ease Friday through the weekend.
Coastal impacts associated with this swell could be significant due to a combination of moderate to fresh northerly (onshore) winds and the peak daily high tide potentially coinciding with the peak surf anticipated Thursday evening.
Surf along south facing shores will remain up slightly through Tuesday due to a small, background south-southwest swell moving through.

HFO Watches/Warnings/Advisories

High Wind Warning until 6 AM HST Tuesday for Big Island Summits.

Data Courtesy of NOAA.gov