Photo Credit: Leosan Miguel

West Side

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 75 to 82. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 62 to 68. Northeast winds 15 to 25 mph with gusts to 45 mph. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 76 to 82. Northeast winds 15 to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

South Side

Today: Breezy. Mostly sunny with isolated showers. Highs around 81. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 63. Northeast winds 20 to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs around 81. Northeast winds 15 to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

North Shore

Today: Breezy. Cloudy with occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 79 near the shore to around 57 near 5000 feet. East winds 15 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Occasional showers. Lows 60 to 67 near the shore to 43 to 49 near 5000 feet. Northeast winds around 20 mph. Chance of rain near 100 percent.

Friday: Mostly cloudy. Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 74 to 79 near the shore to around 57 near 5000 feet. Northeast winds 20 to 25 mph. Chance of rain 90 percent.

Central Maui

Today: Breezy. Partly sunny with scattered showers and slight chance of thunderstorms. Highs 77 to 82. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 61 to 67. Northeast winds 20 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs around 80. Northeast winds 20 to 25 mph. Chance of rain 50 percent.

Upcountry

Today: Mostly cloudy. Breezy. Showers likely and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Ice accumulation of up to one quarter of an inch. Highs 49 to 64. East winds 15 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Occasional showers in the evening, then scattered showers after midnight. Lows around 41 at the visitor center to around 37 at the summit. Northeast winds 15 to 25 mph. Chance of rain near 100 percent.

Friday: Breezy. Mostly sunny with scattered showers. Highs around 52 at the visitor center to around 55 at the summit. Northeast winds 20 to 25 mph. Chance of rain 50 percent.

East Maui

Today: Breezy. Cloudy with occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 79 near the shore to around 57 near 5000 feet. East winds 15 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Occasional showers. Lows 60 to 67 near the shore to 43 to 49 near 5000 feet. Northeast winds around 20 mph. Chance of rain near 100 percent.

Friday: Mostly cloudy. Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 74 to 79 near the shore to around 57 near 5000 feet. Northeast winds 20 to 25 mph. Chance of rain 90 percent.

Lanai City

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 67 to 74. Northeast winds 20 to 25 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows around 63. Northeast winds 20 to 25 mph.

Friday: Sunny and breezy. Highs 67 to 74. Northeast winds 20 to 25 mph.

Kaunakakai

Today: Windy. Mostly sunny with isolated showers. Highs 70 to 81. Northeast winds 20 to 30 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Windy. Scattered showers in the evening. Lows 58 to 70. Northeast winds 25 to 30 mph. Chance of rain 40 percent.

Friday: Sunny and windy. Highs 71 to 81. Northeast winds 25 to 30 mph.

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.

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Data Courtesy of NOAA.gov