Hilo

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 66 near the shore to 47 to 54 at 4000 feet. West winds up to 10 mph. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then isolated showers in the afternoon. Highs around 78 near the shore to around 63 at 4000 feet. Southwest winds up to 10 mph shifting to the east in the afternoon. Gusts up to 30 mph. Chance of rain 70 percent.

Friday Night: Partly cloudy with isolated showers. Lows 58 to 67 near the shore to 47 to 54 at 4000 feet. Southeast winds up to 10 mph shifting to the south after midnight. Chance of rain 20 percent.

Kona

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Haze through the night. Lows 66 to 72 near the shore to 44 to 50 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs 80 to 85 near the shore to around 64 near 5000 feet. South winds up to 10 mph shifting to the west in the afternoon. Chance of rain 30 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Haze through the night. Lows 66 to 72 near the shore to 45 to 50 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 59 to 68 near the shore to 49 to 58 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs around 78 near the shore to 67 to 75 near 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Haze after midnight. Lows 59 to 68 near the shore to 51 to 59 near 3000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Kohala

Tonight: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 59 to 68 near the shore to 49 to 58 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs around 78 near the shore to 67 to 75 near 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Haze after midnight. Lows 59 to 68 near the shore to 51 to 59 near 3000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

South Big Island

Tonight: Partly cloudy. Breezy and haze. Lows around 71 near the shore to around 50 near 5000 feet. Northeast winds up to 20 mph.

Friday: Mostly sunny. Breezy. Haze through the day. Isolated showers in the afternoon. Highs around 82 near the shore to around 64 near 5000 feet. Northeast winds 10 to 25 mph shifting to the east up to 25 mph in the afternoon. Chance of rain 20 percent.

Friday Night: Partly cloudy. Breezy. Haze through the night. Lows around 71 near the shore to around 51 near 5000 feet. Northeast winds 10 to 20 mph.

Puna

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 66 near the shore to 47 to 54 at 4000 feet. West winds up to 10 mph. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then isolated showers in the afternoon. Highs around 78 near the shore to around 63 at 4000 feet. Southwest winds up to 10 mph shifting to the east in the afternoon. Gusts up to 30 mph. Chance of rain 70 percent.

Friday Night: Partly cloudy with isolated showers. Lows 58 to 67 near the shore to 47 to 54 at 4000 feet. Southeast winds up to 10 mph shifting to the south after midnight. Chance of rain 20 percent.

Waikoloa

Tonight: Partly cloudy. Breezy. Lows 66 to 72 near the shore to 46 to 52 above 4000 feet. Southeast winds up to 20 mph.

Friday: Mostly sunny in the morning then becoming partly sunny. Haze. Highs around 82 near the shore to 61 to 69 above 4000 feet. Southeast winds up to 15 mph shifting to the northwest in the afternoon.

Friday Night: Partly cloudy. Haze through the night. Isolated showers after midnight. Lows around 70 near the shore to 47 to 52 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Today will likely be the last day of trade winds, as winds become southeast Friday. A relatively dry and stable air mass will continue to support only light showers focused windward and mauka through the middle of next week. A weak cold front and upper level trough will bring increased moisture and a slight increase in instability early next week, keeping the chance of showers going. These showers will still be mainly windward and mauka. Trades are expected to return in the middle of next week.

Discussion

Skies were partly cloudy across the state this afternoon. Light showers were noted on radar, mainly mauka and windward. The exception was in the Kona region of the Big Island, where afternoon cumulus buildups have developed into isolated showers. The atmosphere is relatively dry at low levels, and stable as well. Trade winds continue to blow today, but should turn and come out of the southeast Friday. These southeast winds are forecast to last into Wednesday of next week.
A ridge of high pressure at the surfaces stretches from southwest to north-northeast of the state this afternoon. And this ridge extends vertically as well, with the upper level ridge axis running pretty much due north. Surrounding this upper level ridge is a pair of troughs. The one to our northeast is associated with the flooding and severe storms along the west coast of the mainland. The one to our northwest will weaken as it approaches, pushing a weak cold front toward Kauai County Saturday night and Sunday. This front will then stall near but most likely just west of the state, before slowly retreating westward Monday. Depending on exactly how far east the front makes it, Kauai County could see a noticeable increase in showers.
The upper trough associated with this front will weaken and remain nearly stationary through Wednesday. This will bring slightly cooler temperatures aloft, help to increase low level moisture due to persistent southeast flow, and therefore help to slightly destabilize the atmosphere. PW values increase slowly through Tuesday before dropping back down Wednesday into Thursday, but remain below normal throughout this process. Therefore, showers will continue to be favored mauka and in windward areas, with an additional increase on southeast-facing shores that may not be traditionally considered windward. Weak ridging aloft is expected to move in late Wednesday and Thursday, and this will help strengthen a surface ridge to the north and should bring back east to northeast trade winds.

Aviation

Trade winds continue through today before gradually weakening and transitioning to ESE tomorrow. Shower activity remains limited through the evening, but overnight and early morning windward and mauka showers are possible. Expect brief MVFR conditions within those showers, and VFR conditions otherwise.
No AIRMETS are in effect at this time.

Marine

Changes with the afternoon forecast package include extending the Small Craft Advisory (SCA) through Friday night. Otherwise little change to the forecast.
Most of the models, high resolution and global models, show SCA level winds remaining in place over the typically windier waters near Maui County and the Big Island into Friday night. With those models in good agreement with today's ASCAT passes, have extended the SCA through Friday night. High pressure remains far north of the islands, and the associated ridge is expected to sink southward and weaken winds Friday night.
A low pressure system far to the northwest of the islands has a cold front associated with it that is expected to enter the northwest offshore waters Saturday. As this front gets closer to the offshore waters, we will see the winds over the coastal waters weaken and veer to a more southeasterly direction. The front itself is expected to bring some thunderstorms to the northwest offshore waters Saturday through Monday. At this time, it looks like the instability that will trigger the thunderstorms will stay north of the coastal waters.
The current moderate, medium period north-northeast (010-030 degrees) swell continues to boost surf heights along north facing shores. This swell is expected to be on the decline Friday. A Marine Weather Statement remains in place for moderate harbor surges at Kahului and Hilo through tonight. A combination of the declining north-northeast swell and a small long period west- northwest swell will keep smaller surf in the forecast this weekend. The next large long period northwest swell is expected over the first half of next week.
Rough and choppy surf along east facing shores will gradually decline as trade winds ease over the next few days. Some wrap around energy from the medium period north-northeast swell will create choppy rough surf conditions along east sides of all islands. Surf along south facing shores will remain very small through the week.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov