Photo Credit: Braden Jarvis

West Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs around 82 near the shore to around 71 above 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 70 near the shore to around 59 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 50 percent.

Washingtons Birthday: Cloudy with scattered showers and isolated thunderstorms. Highs around 82 near the shore to around 70 above 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

South Kaua’i

Today: Mostly cloudy with scattered showers. Highs 78 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 67. East winds 10 to 15 mph. Chance of rain 60 percent.

Washingtons Birthday: Cloudy with scattered showers and isolated thunderstorms. Highs 77 to 83. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs 71 to 77 in the valleys to around 63 above 4000 feet. Southeast winds up to 25 mph shifting to the east 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 60 to 67 in the valleys to around 58 above 4000 feet. Southeast winds 10 to 20 mph. Chance of rain 60 percent.

Washingtons Birthday: Cloudy with scattered showers and isolated thunderstorms. Highs 70 to 76 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 73 to 81. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 62 to 70. East winds 10 to 20 mph. Chance of rain 60 percent.

Washingtons Birthday: Breezy. Cloudy with scattered showers and isolated thunderstorms. Highs 73 to 81. Southeast winds 10 to 20 mph. Chance of rain 40 percent.

East Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Highs 71 to 81. East 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 62 to 71. East winds 10 to 20 mph. Chance of rain 60 percent.

Washingtons Birthday: Breezy. Cloudy with scattered showers and isolated thunderstorms. Highs 70 to 81. East winds 10 to 20 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

The upper level low south of the Hawaiian Islands will continue to slowly drift southeastward and weaken through Monday. A tropical moisture band will linger over the state for the next few days with periods of showers possible. However, the potential for heavier rainfall rates are decreasing statewide. Showers and thunderstorms may redevelop again over the western half of the state from late Monday into Wednesday as another cut off low drops in northwest of the island chain. A surface high pressure ridge building into the region from the northeast will produce breezy to windy easterly trade winds next week, pushing the tropical moisture and showers westward away from the islands from Wednesday onward.

Discussion

An upper level low south of the Hawaiian Islands continues to weaken this morning on satellite imagery. A large convective band is currently developing just east of the low center with the best upper level forcing likely remaining south of the Big Island today. This satellite analysis is consistent with forecast guidance showing both weakening and slow southeast movement trends with the low center. The threat for moderate to heavy rainfall near the Big Island today will decrease significantly over the next 12 to 24 hours.
Periods of rain showers will develop over the Big Island today and any additional rainfall on already saturated ground may lead to rapid runoff, elevated stream flow, and flash flooding concerns. A Flood Watch remains in effect for the Big Island through this afternoon. A Winter Storm Warning also remains in effect for the Big Island Summits through noon today as additional snow and ice remains in the forecast. This warning may become a Winter Weather Advisory later this afternoon as freezing conditions could last into Monday.
Today through Tuesday, the short term weather pattern remains similar in the latest forecast models with good agreement on the transition to decreasing showers trends into Monday. A tropical moisture plume will remain near the islands keeping layered clouds and deeper moisture over the region. However, the position of the most unstable moisture and rainfall activity will shift over the next few days as the weather pattern changes. A high pressure ridge will build slowly into the region from the northeast, bringing trade winds back to the eastern islands and pushing the tropical moisture plume slowly westward from tonight into Monday morning. Expect breezy to windy trade winds over Maui and the Big Island for the first half of next week with passing showers favoring windward and mountain areas. Meanwhile, northwest of the islands, a cut off low will begin to move into the region producing enough southerly flow aloft to pull the tropical moisture plume northward into Kauai and possibly Oahu from Monday night into Wednesday. Expect increasing shower activity during this time period over the western islands with more stable trade wind weather conditions favoring the central and eastern islands in Maui and Hawaii Counties.
Wednesday through Friday, the longer term forecast continues to trend towards a more stable breezy to windy trade wind pattern statewide from Wednesday onward. A narrow upper level trough will develop over the region, producing enough lift for enhanced windward and mountain showers, especially along the eastern slopes of Maui and the Big Island. Therefore, periods of passing showers in strong trade winds are favored over windward and mountain areas. Wind speeds may grow strong enough to exceed wind advisory thresholds for some areas during this time period.

Aviation

An upper-level low pressure system located south of Honolulu will keep the atmosphere unstable across the main Hawaiian Islands today. In addition, abundant deep tropical moisture remains in the vicinity of the islands. An area of layered clouds and showers has been confined to the eastern end of the state since last evening, but there has been a significant decrease in the coverage of rainfall early this morning. Widespread cloudiness with embedded locally heavy showers and isolated thunderstorms continue to be in the forecast for most of the Big Island today. This will likely produce periods of MVFR / localized IFR conditions over portions of the windward Big Island. Elsewhere, clouds and showers will also continue across portions of the smaller islands. This will likely result in periods of MVFR conditions occurring, especially over the higher terrain and north through southeast facing slopes.
AIRMET Sierra for IFR may be cancelled for the windward Big Island later this morning. However, AIRMET Sierra for mountain obscuration will likely be needed for portions of the windward Big Island after this is cancelled. AIRMET Sierra for mountain obscuration also continues for portions of Maui and Kauai. This AIRMET may be added to other islands if mountain obscuration develops later today. AIRMET Zulu also continues for moderate icing in cloud / precipitation in the layer from 14 to 30 kft from Molokai to the Big Island.
A broad surface high pressure system is centered far north- northeast of the islands, which is producing light to locally moderate east to southeast background winds in the vicinity of the state early this morning. The latest forecast guidance appears to indicate the background flow will strengthen later today or tonight. Therefore, locally breezy conditions may develop by this afternoon or evening. We will monitor observations, since AIRMET Tango may be needed for low-level moderate turbulence over and downwind of the higher terrain on some, or possibly all, of the islands later today.

Marine

Strong high pressure well northeast of the state will keep strong to near-gale force east to southeast winds in place across most waters through the remainder of the weekend, with lighter winds continuing over the leeward waters around Kauai and Oahu. Winds will become more easterly next week, with strong to near-gale force winds gradually expanding to the entire marine area as the week progresses. A Small Craft Advisory (SCA) is now in effect for most waters through Thursday, due to winds/seas or a combination of the two.
Surf along east facing shores will remain rough for the next week due to persistent strong east to southeast winds over and upstream of the islands. East shore surf will likely build back to advisory levels Monday night through late in the week.
A series of small northwest swells will keep some small and well below normal surf in place along north and west facing shores through late this week. South shore surf will remain minimal for the foreseeable future.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for the Big Island.
Winter Storm Warning until noon HST today for Big Island Summits.
Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov