Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs around 79 near the shore to around 67 above 3000 feet. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Isolated showers after midnight. Lows around 66 near the shore to around 55 above 3000 feet. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Friday: Sunny and breezy. Highs around 80 near the shore to around 67 above 3000 feet. Northeast winds 15 to 20 mph.

South Kaua’i

Today: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs around 78. Northeast winds 20 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 69. Northeast winds 20 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 81. Northeast winds 20 to 25 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Mostly cloudy. Windy. Occasional showers in the morning, then showers likely in the afternoon. Highs 66 to 74 in the valleys to around 60 above 4000 feet. Northeast winds 15 to 30 mph. Chance of rain 90 percent.

Tonight: Windy. Mostly cloudy with showers likely. Lows 55 to 60 in the valleys to around 49 above 4000 feet. Northeast winds 20 to 30 mph. Chance of rain 70 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Windy. Scattered showers. Highs 66 to 74 in the valleys to around 61 above 4000 feet. Northeast winds 20 to 30 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy. Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 71 to 78. Northeast winds 15 to 20 mph. Chance of rain 80 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 58 to 67. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Friday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 71 to 79. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 71 to 78. Northeast winds 15 to 20 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 56 to 69. Northeast winds 20 to 25 mph. Chance of rain 70 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 71 to 79. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will remain locally strong and gusty through the weekend. Fewer showers are expected over Kauai and Oahu the next couple of the days, while the Big Island and Maui will continue to see a fair amount of windward showers. Another period of enhanced rainfall is possible statewide starting late Monday.

Discussion

Active night of weather as areas of increased moisture riding in on the strong trade wind flow interacted with island terrain and instability associated with a low aloft to bring widespread heavy showers, and scattered thunderstorms with gusty winds. Water vapor imagery and model analyses indicate a closed low aloft immediately over the island chain, with attendant 500 mb temperatures near -16C. This is supporting steep low- and mid-level lapse rates which in turn promote the development of strong updrafts, leading to charge separation/lightning in the strongest cells. Shower coverage and intensity has generally trended down over the last couple of hours however.
A pair of surface high pressure cells are located far NE and NW of the islands, with the associated low-level pressure gradient supporting strong and gusty trade winds. The deep moisture and cold temperatures aloft have led to periods of snowfall and freezing rain overnight on the Big Island Summits, where a Winter Weather Advisory remains in effect today.
A trend toward fewer (and less intense) showers is expected today for some areas as the low aloft weakens/moves away to the SW, allowing mid-level temperatures to warm over the area. A N-S gradient in PWAT is also expected to develop, dropping below 1″ over Kauai and Oahu, while remaining near 1.4″ over the Big Island. This will likely lead to continued wet conditions over windward Big Island and possibly Maui, with fewer windward showers elsewhere. A lingering trough aloft will ensure that the returning subsidence inversion is weakened/elevated over the next couple of days. Additionally, high clouds will thicken over S parts of the state over the next couple of days.
Guidance is increasingly indicating that the destabilizing low aloft will move back over the islands from the SW early next week, bringing a statewide increase in showers from Monday night into Wednesday. Mid-level temperatures are not expected to be as cold as currently, making thunderstorms less likely, but heavy showers look possible again.
A front passing well N of the area will lead to a slight weakness in the surface ridge today, which may allow trade wind speeds to ease ever so subtly. As the high to the NW builds slowly eastward, NE winds are expected to strengthen again tonight, with the slow-moving high supporting breezy to locally windy conditions through the weekend. The high will then move quickly NE away from the area early next week as a strong low/front fill the central N Pacific, with trade winds weakening Tuesday into Wednesday. The front is currently expected to move down the island chain next Wednesday/Thursday, with a fair amount of model agreement on the timing. Strong N winds will usher a cool air mass over the islands after the front passes, if current guidance were to verify.

Aviation

A strong high pressure system building in north of the islands will continue to produce breezy to locally windy trade winds across the Hawaiian Islands into Saturday. An upper level low will also produce periods of unstable showers and with gusty winds affecting all islands through today. Isolated thunderstorms are possible for Maui and the Big Island this morning.
AIRMET Sierra for mountain obscuration remains in effect for north through east section Kauai, Oahu, Molokai, Maui and the Big Island. This AIRMET will continue into the morning hours.
AIRMET Tango for moderate to locally severe turbulence over and south through west of island mountains remains in effect. PIREP's with severe turbulence were reported this evening near the island of Lanai. This AIRMET will likely continue through the rest of the week.

Marine

High pressure north of the state will slowly drift eastward over the next several days maintaining near strong to near gale force trade winds across all coastal water zones through the weekend. Another high pressure will build north of the islands towards the end of the week, with little change in wind speeds. A Small Craft Advisory (SCA) for all nearshore coastal zones has been issued through Saturday. As surface pressure gradient tightens Friday through this weekend, gale conditions may develop in the typical windier channels surrounding the Big Island and Maui.
An upper level trough will remain stagnant over the islands today and bring enhanced trade showers and isolated thunderstorms to the region, though mainly concentrated Big Island and Maui waters. These showers and storms may produce brief periods of locally strong winds and lower visibility. A more typical trade wind pattern will return by Friday as the trough weakens.
Persistent fresh to strong trades will continue to generate rough, choppy surf along east-facing shores through the week. Despite these very rough conditions, east surf is expected to remain under High Surf Advisory heights. A small, medium period northwest (310 degree) swell will hold today before declining Friday. A moderate, medium period northwest (320 degree) swell is scheduled to build Friday night, and peak on Saturday near High Surf Advisory levels.

HFO Watches/Warnings/Advisories

Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 AM HST Saturday for all Hawaiian waters.

Data Courtesy of NOAA.gov