West Side

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

Tonight: Partly cloudy with isolated showers. Lows 66 to 73. East winds 10 to 15 mph. Chance of rain 20 percent.

Saturday: Sunny. Isolated showers in the morning. Highs 78 to 83. East winds up to 15 mph. Chance of rain 20 percent.

South Side

Today: Sunny. Highs around 86. Northwest winds up to 15 mph.

Tonight: Mostly clear. Isolated showers in the evening. Lows 65 to 74. North winds up to 15 mph. Chance of rain 20 percent.

Saturday: Sunny. Highs around 86. North winds up to 15 mph.

North Shore

Today: Mostly cloudy. Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 63 near 5000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71 near the shore to around 51 near 5000 feet. East winds up to 20 mph shifting to the southeast 10 to 20 mph after midnight. Chance of rain 50 percent.

Saturday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 80 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Central Maui

Today: Breezy. Sunny with isolated showers. Highs 80 to 87. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows 65 to 70. Northeast winds 10 to 15 mph shifting to the east after midnight. Chance of rain 20 percent.

Saturday: Sunny and breezy. Highs 81 to 86. Northeast winds up to 20 mph.

Upcountry

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 59 at the visitor center to around 65 at the summit. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 46 at the visitor center to around 42 at the summit. East winds up to 15 mph. Chance of rain 50 percent.

Saturday: Sunny with isolated showers. Highs around 60 at the visitor center to around 65 at the summit. East winds up to 10 mph. Chance of rain 20 percent.

East Maui

Today: Mostly cloudy. Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 63 near 5000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71 near the shore to around 51 near 5000 feet. East winds up to 20 mph shifting to the southeast 10 to 20 mph after midnight. Chance of rain 50 percent.

Saturday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 80 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Lanai City

Today: Mostly sunny with isolated showers. Highs 72 to 80. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 65. Northeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

Saturday: Sunny. Highs 71 to 79. Northeast winds up to 15 mph.

Kaunakakai

Today: Breezy. Mostly sunny with isolated showers. Highs 69 to 86. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 58 to 72. East winds 10 to 15 mph. Chance of rain 20 percent.

Saturday: Sunny. Highs 69 to 86. East winds 10 to 15 mph.

Detailed Forecast

Synopsis

Light to occasionally breezy easterlies will gradually drop off through the day. Today's highest rain chances will be over windward Big Island and the island of Maui. A dry weekend for many with limited clouds and infrequent showers focusing along upslope windward mauka mainly overnight and leeward Big Island during the day.

Discussion

The upper trough west of the islands is weakening and continuing to move north as it encounters a large upper ridge northeast of the region this morning. The surface pressure gradient from the surface high centered 1,400 miles northeast of Oahu is tight enough across the region to support moderate to locally strong offshore easterlies. These winds will persist through the afternoon and may become occasionally gusty across many windward exposures and around higher terrain through most of the day. The latest slug of moisture has advanced across Big Island and dropped a solid quarter to a half an inch of rain along windward Mauna Kea and Mauna Loa this morning. Shortwave IR imagery showing less consolidation of thicker, warmer clouds east of the state. This verifies the global deterministic guidance of a drying atmosphere. There is one batch of higher moisture/deeper clouds southeast of Big Island that will come across later this morning. This will introduce return showers to windward Big Island through the early afternoon. The upper trough and associated southern branch of the polar jet are both losing their punch. The trough will wash out along its northeast journey around upper to mid level ridging east of the state and open the door for prevailing dry conditions this weekend. This morning's Lihue sounding provided more than a reasonable doubt indication of drier weather (Hilo's data is skewed moist as the balloon ascended through showers). A near 6-7k ft inversion will not be deep enough to support much in the way of organized cells. The only measurable rain will fall upslope windward or within higher elevations into the mid to late afternoon. Ridging will build in from the west southwest and envelope the state early next week. Subtle weakening of the surface high off the U.S West Coast early next week will maintain gentle to breezy trades through the middle of next week. Ridging will introduce a thick slab of subsident, very dry air over the islands that will equate to a shallower boundary layer; more sun with little to no mentionable light precipitation. Confidence is moderately high of a drier beginning of the week under seasonable trades as the majority of the NWP model ensemble members maintain very low to no QPF over Hawaii and its surrounding waters next week.
The weather pattern may undergo change late next week as the next North Pacific trough moves across the central basin. The leading front appears to behave the same way as this current one…stalling west of Kauai as the bulk of the upper level support/energy is directed northeastward. There may be a diffuse lower level boundary that is pushed into the central waters sometime next Friday or Saturday. The only way a weak front will advance into our waters is if shortwave energy dives into the weakening trough and provides the needed umph to progress a light wind shift eastward. Since both long range deterministic models are way out of phase and disagree on the evolution of this next feature, confidence is extremely low on any significantly impactful weather by Day 7. The best signal may be a very weak wind field if the islands fall into a pressure col, allowing localized breezes to play a more dominant role. This scenario would mean more leeward and further interior showers but little rain to ease the pain of this moderate to severe drought.

Aviation

VFR conditions with gradually weakening easterlies will prevail today and tonight. Cats will briefly fall into MVFR within more moderate passing showers over Hilo or possibly Molokai or Lanai. Possible brief mountain obscuration over the eastern half of the state this morning.
No AIRMETs are in effect or are anticipated in the short term.

Marine

A trough west of Kauai will gradually weaken and retrograde westward, away from the islands. Meanwhile, a ridge of surface high pressure building northeast of the state will allow for moderate to locally strong east to east southeast winds to persist through early Saturday. A Small Craft Advisory (SCA) remains in effect through 6 AM Saturday morning for most of the marine zones surrounding the Big Island and Maui County and western zones around Kauai and Oahu for winds and seas.
A moderate, medium period northwest swell (320 degrees) has filled in across north and west facing shores bringing surf heights above High Surf Advisory (HSA) criteria. This swell is expected to peak this morning, then ease into the weekend. A HSA is in effect for north and west facing shores of Kauai, Oahu and Molokai and north shores of Maui. This swell will hold today, then gradually fade and veer to the north northwest through the remainder of the weekend and into early next week and bring below average surf for December for north and west facing shores.
East shore surf will gradually build and become choppy today as trade winds increase. Expect minimal background energy for south facing shores through much of the week.
Peak monthly tides combined with water levels that are running higher than predicted will likely lead to minor flooding along the shoreline and in low-lying coastal areas. Coastal flooding is possible around the daily peak tide, which will be during the early morning hours. This could also magnify effects of the high surf on coastal areas along north and west facing shores around the same time frame.

Fire weather

Critical fire weather conditions are not expected this week. Light to occasionally moderate trades today, but winds will remain below the critical fire weather threshold. The lack of any significant rain will exacerbate already dry conditions across the entire state. The inversion morning sloped from around 6,500 ft at Lihue to around 9,000 ft over Hilo.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov