West Side

Today: Mostly sunny with isolated showers. Highs 80 to 86. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 68 to 76. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny. Breezy. Isolated showers in the morning. Highs around 84. East winds 10 to 20 mph. Chance of rain 20 percent.

South Side

Today: Sunny. Highs around 89. North winds 10 to 15 mph.

Tonight: Mostly clear. Isolated showers in the evening. Lows 70 to 76. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Sunny. Highs around 90. North winds 10 to 15 mph.

North Shore

Today: Partly sunny with scattered showers. Highs 80 to 86 near the shore to around 67 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 73 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 80 to 86 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Central Maui

Today: Mostly sunny. Isolated showers in the afternoon. Highs 81 to 89. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Sunny and breezy. Isolated showers in the morning. Highs 83 to 90. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny with isolated showers. Highs around 66 at the visitor center to around 69 at the summit. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers. Lows around 50 at the visitor center to around 46 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 65 at the visitor center to around 57 at the summit. East winds 10 to 15 mph. Chance of rain 40 percent.

East Maui

Today: Partly sunny with scattered showers. Highs 80 to 86 near the shore to around 67 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 73 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 80 to 86 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Lanai City

Today: Sunny. Highs 73 to 82. Northeast winds 10 to 15 mph.

Tonight: Mostly clear. Lows 64 to 69. Northeast winds 10 to 15 mph.

Friday: Sunny. Highs 74 to 82. Northeast winds 10 to 15 mph.

Kaunakakai

Today: Sunny with isolated showers. Highs 72 to 90. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows 62 to 75. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Sunny and breezy. Isolated showers in the morning. Highs 73 to 90. East winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A near static and quiet weather pattern will undergo change the next few days as rain chances increase going into and through the weekend. The western half of the state will likely experience a more wet weekend while light to locally breezy regional trade winds remain in place through the end of the week. Today's showers will focus along windward exposures, upslope mauka and within higher elevations. Stable and drier weather is expected to return early next week.

Discussion (corrected at 415 am)

The current synoptic summertime pattern remains entrenched over the Hawaiian Islands. This being of high pressure ridging at all levels positioned north and northeast of the state. Light, random showers passing within the trade belt has wettened many windward locales with brief light rain episodes. The windward slopes of Big Island's Hamakua, Hilo and Puna regions have received the most 24 hour rainfall of typically a quarter of an inch or less. The remainder of the state has picked up no more than a few hundredths to a tenth of an inch over east-facing regions while many leeward areas have remained bone dry. A surge of higher mid to low level moisture passing through today will thicken up clouds and increase primarily windward and upslope mauka/high elevation shower activity. The caveat will be along more wind-protected Big Island Kona slopes whereas the enhanced afternoon sea breeze will increase upslope clouds and areal rain chances. The large scale downstream pressure gradient from a 1035 mb high centered near 45N145W has been tight enough to produce statewide interior light to breezy trades. Downslope or channeled winds have been locally strong over such areas as the central Maui Valley (Kealaloloa Ridge) and North Kohala's northernmost tip (Upolu Point) where winds of 25 to 30 mph sustained with gusts to over 40 mph have been commonplace the past several days. Little change in the strength and position of the surface high will guarantee another few days of this wind behavior.
Geopotential heights will begin to gradually fall from the northwest as a weak mid to upper low or troughing develops west of the islands the next few days. Height falls of around 400 meters and increased 500 mb vorticity, along with a surge of unseasonably higher moisture (1.6 inch pwats) advecting in from the east, will decrease stability and boost rain chances mainly north of 21N…better focusing the higher precipitation over Oahu and Kauai from late Friday through early Sunday. Deterministic guidance is forecasting deepening moisture where yesterday's 4k ft resident boundary layer depth (inversion heights) should double to around 8k ft by Saturday. The majority of the GFS and EC ensemble guidance QPF members depict a distinct swath of higher rain paralleling near 20N latitude. While confidence is moderately high that more western islands will experience a more wet (than dry) weekend, the chance of thunderstorms and confidence of occurrence remains low. NWP guidance does not cool upper level temperatures enough (around minus 7 deg C at 500 mb) to provide a strong enough instability signal to place thunder in Kauai or Oahu's weekend forecast. The proximity of the low across the far northern maritime will likely be the impetus to isolated offshore storms this weekend. As of now, the highest confidence lays in higher rain probabilities N of 20N with periods of heavy rain from as early as tomorrow (Friday) night through as late as early Monday. The timing of the heaviest rain will depend upon the evolution of the upper low in accordance with the greatest moisture advection.
A more stable summer-like trade wind pattern is expected to return by late Monday. As greater moisture exits stage left on Monday, a drier air mass in its wake will envelope the eastern half of the state. The upper level low will move further away, northeast of the region…weakening into a trough as ridging expands in from the south.

Aviation

Moderate to locally breezy trades through tomorrow. Low cigs and SHRA should mainly impact windward and mauka locations, as well as the South Kona slopes of the Big Island. Trades will ease slightly Friday and Saturday, and SHRA activity may increase as the atmosphere becomes less stable.
AIRMET Sierra is in effect for mtn obsc for windward sections of all islands. Conds should improve in the morning hours.
AIRMET Tango is in effect for low level turb blw 070 downwind of island terrain.

Marine

High pressure will remain far northeast of the state through the rest of the week. Fresh to locally strong trades will persist through the rest of today, then drop slightly as a weak low level trough develops in the easterly flow and moves across the state tonight into the weekend. A Small Craft Advisory (SCA) remains in effect for the typical windy areas around Maui County and the Big Island through 6AM Friday.
A fading medium period south swell combined with a fading south- southeast swell will maintain below summer average surf on the south facing shores through today. A slight bump in surf is expected this weekend as a new long-period southwest swell arrives from the Tasman Sea, along with a new small short-period south-southeast swell. The Tasman swell is expected to peak on Saturday, with surf heights topping near the summer averages before gradually declining into early next week.
Surf along east facing shores will continue to remain rough and choppy due to the fresh to locally strong trade winds and a small short-period northeast swell that is expected to fill in this weekend. Surf along north facing shores will remain nearly flat through the weekend.
Minor coastal flooding along the shoreline and in low-lying coastal areas will be possible around the daily high tide starting Monday of next week due to peak monthly tides and higher than predicted water levels at select locations.

Fire weather

Fire weather concerns will lower the next few days as a more wet pattern develops across the state. Trade winds will remain light to locally breezy through the day before subtly weakening this weekend. A higher frequency of showers is expected from late tonight into Friday and this will hold through the weekend. Drier, more stable weather is expected to return early next week. This may increase the fire weather threat over more leeward areas that do not receive the benefit of significant weekend rains.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov