Photo Credit: Brendan Stephen

West Kaua’i

Today: Windy. Mostly sunny with isolated showers. Highs around 76 near the shore to around 64 above 3000 feet. East winds up to 30 mph increasing to 10 to 30 mph in the afternoon. Chance of rain 20 percent.

Tonight: Windy. Partly cloudy with isolated showers. Lows around 66 near the shore to around 55 above 3000 feet. East winds 15 to 30 mph. Chance of rain 20 percent.

Monday: Windy. Mostly sunny with isolated showers. Highs around 77 near the shore to around 65 above 3000 feet. East winds 15 to 30 mph. Chance of rain 20 percent.

South Kaua’i

Today: Windy. Partly sunny with scattered showers. Highs around 75. Northeast winds 15 to 30 mph shifting to the east 25 to 30 mph in the afternoon. Chance of rain 50 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows 62 to 67. East winds 25 to 30 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly cloudy with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs around 76. East winds 20 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly cloudy. Windy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 63 to 71 in the valleys to around 58 above 4000 feet. East winds 10 to 30 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Windy. Numerous showers in the evening, then showers after midnight. Lows 55 to 60 in the valleys to around 49 above 4000 feet. East winds 20 to 30 mph. Chance of rain 90 percent.

Monday: Windy. Cloudy with showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 64 to 72 in the valleys to around 59 above 4000 feet. East winds 15 to 30 mph. Chance of rain 80 percent.

North Kaua’i

Today: Windy. Partly sunny with scattered showers. Highs 68 to 75. East winds up to 25 mph increasing to 10 to 30 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 58 to 67. East winds 10 to 25 mph. Chance of rain 50 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Windy. Scattered showers. Highs 69 to 76. East winds 10 to 30 mph. Chance of rain 50 percent.

East Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 68 to 75. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 56 to 68. East winds 20 to 25 mph. Chance of rain 70 percent.

Monday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 76. East winds 20 to 25 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A strong high pressure system located north of the Hawaiian Islands will continue to produce breezy to windy northeasterly to easterly trades across the state lasting into Tuesday. Trade wind showers will increase in coverage, mainly over windward and mountain areas with some of the stronger showers spilling over to the leeward slopes of each island. The high pressure center north of the islands will slowly drift eastward starting on Tuesday, trade wind speeds will slowly decrease from Tuesday onward. Another cold front approaching the state from the northwest will cause the winds to weaken from Friday into next weekend and blow from a more southeasterly direction.

Discussion

This mornings satellite imagery shows bands of fairly stable stratocumulus clouds moving into the windward and mountain slopes of each island on the breezy to windy trade winds. Upper air balloon soundings from Lihue and Hilo at 2 AM HST this morning show subsidence inversion heights around 6,000 to 7,500 feet above sea level. Strong trade winds will push clouds up the windward mountain slopes and produce scattered to numerous showers along north through east sections of each island. A few of the stronger showers will drift over leeward areas with more isolated to scattered shower coverage. Local radar imagery supports this rainfall coverage with light to moderate showers moving into windward slopes this morning. Shower coverage will decrease slightly after sunrise due to diurnal daytime stabilizing trends.
Cool and windy weather remains in the forecast statewide through Monday due to a strong high pressure system in place north of the island chain. Colder island air temperatures and drier humidity levels are due to a cooler air mass over the Hawaii region with dew point temperatures in the mid 50's today and tonight. Dew point temperatures in the 50's indicates less moisture in the lower atmosphere, which allows surface air temperatures to cool off faster during the overnight hours. This lack of a 'moisture blanket' creates colder overnight to early morning low temperatures. Expect cooler weather to gradually improve from today onward as the air mass is slowly modified by the warmer ocean waters.
Advisory level nuisance wind impacts will continue across the state into Monday as the strong high pressure system north of the islands keeps windy easterly trade winds in the forecast. The current Wind Advisory remains was extended in time now in effect through Monday afternoon. Wind speeds will slowly decrease over the western islands on Monday, wind speeds may decrease below advisory thresholds over Kauai and possibly Oahu, therefore the wind advisory coverage may need to be trimmed back for some of the western islands by Monday morning. Otherwise expect gradually decreasing wind speeds from Tuesday onward as the high pressure system begins to drift eastward away from the Hawaii region. Trade winds will blow at moderate to locally breezy levels by Thursday, and then weaken to light to moderate levels with hybrid sea breezes over each island from Friday into next weekend.
Rainfall trends will increase mainly over windward and mountain areas, favoring the overnight to early morning hours. Most of these showers will be light to moderate intensity levels as subsidence inversion heights are forecast to remain in the 5,000 to 8,000 foot range through much of next week. Some of the stronger windward showers will spill over into leeward areas of each island with isolated leeward shower coverage favoring the overnight to early morning hours.

Aviation

An area of strong surface high pressure north of the state will help maintain breezy to windy northeast to east flow through the forecast period. Thus, expect tempo moderate turbulence near the lee of the mountains. See AIRMET TANGO below.
Isolated to scattered showers will mainly affect windward locations and bring brief periods of of MVFR ceilings and visibility. Otherwise, dry conditions and partly cloudy skies will prevail for leeward locations.
AIRMET TANGO remains in effect below 10000 feet for moderate turbulence downwind of all islands with little change through this evening.

Marine

Strong- to gale-force easterly trades associated with high pressure north of the state will continue through Monday, then shift out of the east-southeast and weaken into the fresh to strong category Tuesday through midweek. A combination of rough, short-period wind waves in response to these winds, a large, north-northeast swell moving through, and an arriving northwest swell later today support hazardous marine conditions persisting across all Hawaiian waters through the first half of the week. Expect gales over the typically windier channels between Maui County and the Big Island, the leeward waters of Maui County, Maalaea Bay (north winds), and over the waters around South Point of the Big Island through Monday. The winds and seas should ease late in the week as the ridge weakens to the north.
Surf along exposed north and east facing shores will remain rough due to a mix of locally-driven wind waves and a medium-period north-northeast (020 deg) swell moving through. Surf will hold at warning levels for eastern exposures today, then likely dip to advisory levels tonight as the north-northeast swell lowers slightly. Exposed north facing shores on the smaller islands will remain around the advisory level today.
Surf along north and west facing shores will trend up later today through tonight as a long-period northwest (310-320 deg) swell arrives. This swell will peak on Monday (advisory levels), then ease Tuesday through the second half of the week. Models show the next significant northwest swell arriving late next weekend.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST Monday for all Hawaiian Islands.
High Surf Warning until 6 PM HST this evening for east facing shores of Kauai, Oahu, Molokai, Maui, and the Big Island.
High Surf Advisory until 6 PM HST this evening for Niihau, Kauai Leeward, Oahu North Shore, Maui Leeward West, Kohala, Kauai North, Molokai Windward, Molokai North, Maui Central Valley North.
Gale Warning until 6 AM HST Monday for Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Tuesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.

Data Courtesy of NOAA.gov