Hilo

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 64 to 69 near the shore to around 51 at 4000 feet. North winds up to 20 mph. Chance of rain 80 percent.

Wednesday: Mostly cloudy with numerous showers. Highs 76 to 82 near the shore to 62 to 67 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 64 to 69 near the shore to around 51 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 80 percent.

Kona

Tonight: Mostly clear. Isolated showers in the evening. Lows 68 to 73 near the shore to around 52 near 5000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the afternoon. Highs around 81 near the shore to around 63 near 5000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows 68 to 73 near the shore to around 52 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Waimea

Tonight: Windy. Mostly cloudy with scattered showers. Lows around 66 near the shore to 52 to 59 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs around 78 near the shore to 66 to 73 near 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows around 66 near the shore to 52 to 59 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Kohala

Tonight: Windy. Mostly cloudy with scattered showers. Lows around 66 near the shore to 52 to 59 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs around 78 near the shore to 66 to 73 near 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows around 66 near the shore to 52 to 59 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly clear. Breezy. Lows 65 to 72 near the shore to around 51 near 5000 feet. Northeast winds up to 25 mph with gusts to 50 mph.

Wednesday: Sunny and windy. Highs around 81 near the shore to around 67 near 5000 feet. East winds 10 to 30 mph.

Wednesday Night: Partly cloudy. Breezy. Isolated showers in the evening. Haze through the night. Lows 65 to 72 near the shore to around 51 near 5000 feet. East winds 15 to 25 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 64 to 69 near the shore to around 51 at 4000 feet. North winds up to 20 mph. Chance of rain 80 percent.

Wednesday: Mostly cloudy with numerous showers. Highs 76 to 82 near the shore to 62 to 67 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 64 to 69 near the shore to around 51 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 80 percent.

Waikoloa

Tonight: Mostly clear. Windy. Lows 67 to 73 near the shore to 48 to 55 above 4000 feet. East winds up to 30 mph with gusts to 50 mph.

Wednesday: Sunny and breezy. Highs around 83 near the shore to 64 to 69 above 4000 feet. Northeast winds up to 20 mph.

Wednesday Night: Mostly clear. Isolated showers in the evening. Lows 67 to 73 near the shore to 48 to 55 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy to windy trades will persist through midweek and deliver periods of clouds and showers to windward and mauka areas. Then trades will gradually weaken through the weekend to become moderate to locally breezy and allow for some sea breeze activity over leeward areas. An upper level low moving into the Hawaii Region from the northwest may enhance shower activity across the state from Saturday into early next week.

Discussion

Low clouds continue to be seen streaming into windward and mauka areas on visible satellite imagery this afternoon. Shower activity is less than this morning, but radar is still showing isolated to scattered light showers moving in quickly on the breezy to windy trades. The surface high and mid-level ridge positioned north of the state will continue to sag south and increase the atmospheric stability over the main Hawaiian Islands through Thursday, which will help to damper shower activity some. Even so, batches of moisture caught up in the trades will still deliver light showers to windward and mauka areas, particularly during the late night to early morning periods.
The main forecast focus for the short term period continues to be on the strengthening trade winds. As the strong high pressure system to the north continues to gradually shift south, the pressure gradient will remain tight across the state and temperature inversion heights will fall. This afternoon's upper air soundings confirm this with the inversion dropping by about 1000 feet at Lihue. These conditions will help to funnel stronger trade winds across the state. The strongest winds are expected to remain across the more typical terrain enhanced leeward Maui County and Big Island areas, where a Wind Advisory is in effect through 6 AM tomorrow morning for surface wind speeds expected to exceed 30 mph with gusts to 44 mph or greater. Trades will remain breezy to windy through tomorrow (with winds expected to be just shy of Wind Advisory criteria), then gradually decline through the weekend, as the center of the surface high moves closer to the state then off to the east as a front/trough approaches from the northwest, weakening the local pressure gradient.
As alluded to above, models show a shortwave trough approaching the state from the northwest this weekend with its attendant cold front pushing the surface ridge further off to the east and shifting the trade winds out of the east-southeast. With trade winds expected to be in the moderate to breezy range and this slight shift in direction, isolated sea breeze activity will be possible, allowing clouds and a few showers to develop over leeward areas in the afternoons. Instability will increase as a mid-level low moves over the Big Island from the southeast and the shortwave trough approaches from the northwest and forms a cutoff low. Both of these upper level features will bring height falls and cooler temperatures aloft. This increasing instability combined with enhanced moisture riding in on the trades from the east and even more moisture moving in from the west may lead to enhanced shower activity across the state, with moderate to locally heavy rain possible. Thunderstorms will also be possible, but will likely stick close to the cold core low where the instability will be greatest, near the western end of the state. The main limiting factor seems to be the lack of any well-defined lifting mechanisms at the surface, since the front will have dissipated before reaching the state. With this being the case, enhanced shower activity will likely be focused over the windward sides of island terrain where orographic lift can do its thing, or along any convergent island plume bands that may form and drift over islands further downstream if there is enough of a southeasterly component in the low-level steering flow. These unsettled weather conditions may last into early next week as model guidance suggests that moisture and instability will linger.

Aviation

High pressure north of the islands will maintain breezy to strong trade winds across the region into tomorrow. AIRMET Tango remains in effect for moderate low level mechanical turbulence to the lee of the mountains. As breezy trades are expected to persist, this AIRMET will likely remain in place over the next couple of days.
Predominantly VFR conditions are expected into tomorrow, with some brief IFR in passing trade wind clouds and showers. As additional cloud and shower bands pass through the islands overnight in the trade wind flow, there may be a need for AIRMET Sierra for mountain obscuration.

Marine

High pressure centered approximately 1,000 nautical miles north of Oahu is still maintaining a very tight pressure gradient between itself and lower equatorial pressure. This will continue to result in strong trade winds the next few days. As this high moves east southeast through the middle of the week, the downstream pressure gradient will be tight enough to support areawide fresh to local gale force easterlies. Today's ASCAT satellite pass did verify that eastern island channels were experiencing gale force winds. Very strong to gale force trades are likely, especially in gust, into early tomorrow morning across the notoriously windier bays and channels surrounding Maui County and Big Island, as well as south of Big Island. A Gale Warning is in effect for Maalea Bay and the Pailolo and Alenuihaha Channels with a Small Craft Advisory in effect for the remaining waters through early tomorrow morning. Trades will remain fresh to locally strong through Friday. High pressure moving further off to the northeast late in the week, with weak troughing developing west of the state, will weaken veering east southeast winds.
A moderate size, medium to long period north northwest (330 degree) swell will arrive overnight into early tomorrow morning. This swell will peak through the day tomorrow, increasing the highest north and west-facing shore surf to near advisory. A similar sized west northwest (300 to 320 degree) swell is scheduled to arrive Thursday night and peak Friday. This swell will maintain slightly above head to double head high surf along many better exposed north-facing shores before dropping through the weekend.
Agitated, rough east seas will persist as a result of days of strong trade winds over and upstream of the islands. Strengthened trades through mid week will push this wind wave-driven swell to near advisory levels.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 AM HST Wednesday for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Lanai Windward, Lanai Leeward, Maui Central Valley North, Maui Central Valley South, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Small Craft Advisory until 6 AM HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Warning until 6 AM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

Data Courtesy of NOAA.gov