Hilo

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 68 at 4000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 64 near the shore to around 53 at 4000 feet. East winds up to 10 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Friday: Partly sunny with numerous showers. Highs around 79 near the shore to around 69 at 4000 feet. Northwest winds up to 15 mph shifting to the east in the afternoon. Chance of rain 70 percent.

Kona

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 77 to 82 near the shore to around 70 near 5000 feet. North winds up to 10 mph shifting to the west in the afternoon. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 66 near the shore to around 54 near 5000 feet. Light winds. Chance of rain 30 percent.

Friday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 78 to 83 near the shore to around 71 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Waimea

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 78 near the shore to 71 to 76 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 63 near the shore to 52 to 58 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 78 near the shore to 71 to 77 near 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Kohala

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 78 near the shore to 71 to 76 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 63 near the shore to 52 to 58 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 78 near the shore to 71 to 77 near 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to around 71 near 5000 feet. East winds up to 25 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 66 near the shore to around 53 near 5000 feet. Northeast winds up to 25 mph increasing to 10 to 25 mph after midnight. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to around 72 near 5000 feet. East winds 10 to 25 mph. Chance of rain 40 percent.

Puna

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 68 at 4000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 64 near the shore to around 53 at 4000 feet. East winds up to 10 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Friday: Partly sunny with numerous showers. Highs around 79 near the shore to around 69 at 4000 feet. Northwest winds up to 15 mph shifting to the east in the afternoon. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 79 near the shore to 67 to 72 above 4000 feet. East winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 67 near the shore to 50 to 56 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 68 to 73 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Gusts up to 40 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy east to east-southeast trades will prevail during the next couple days. Rainfall chances will remain highest over windward and mauka locations, particularly during the overnight and early morning hours, with afternoon showers possible over leeward areas each day. Increasing moisture and a return of breezy easterly trades will support greater windward shower coverage over the weekend through the middle of next week.

Discussion

Currently at the surface, a 1034 mb high is centered around 1250 miles north of Honolulu, while a 1002 mb low is positioned around 1050 miles west-northwest of Kauai. Moderate easterly trade winds prevail in unsheltered sections of the island chain early this morning. Infrared satellite imagery shows mostly cloudy conditions across much of the state. Radar imagery shows scattered to numerous showers moving into windward slopes and coasts, with quite a few decaying showers spilling into leeward communities. Main short term focus revolves around trade wind trends and rain chances during the next few days.
High pressure will strengthen as it remains nearly anchored well north of the islands today through Friday, while a low west- northwest of the state shifts northeastward to a location between 800 and 1000 miles northwest of Kauai. A slight strengthening of the trade winds is expected during this time, although they will generally hold at moderate to locally breezy levels. Due to the east-southeast boundary layer flow, some localized leeward sea breezes will be possible in the more sheltered leeward areas each afternoon as well. The low will weaken and eventually dampen into a trough over the weekend, while the strong high to the distant north settles southward and closer to the island chain. This will ramp the trades up to breezy levels statewide and shift the direction around to a more typical east-northeasterly direction. The strong high will hold north of the state early next week, before being reinforced by a new strong high to the distant north around the middle of next week. Breezy trades are expected to continue early next week, with windy conditions possible at times.
As for the remaining weather details, little change in the overall weather pattern is expected through Friday. Showers will favor windward slopes and coasts. Decaying showers will reach leeward communities at times, and a few leeward showers also developing each afternoon with the assistance of localized sea breezes.
There remains some uncertainty on how far east a front will make it late in the week, with the GFS remaining less progressive and further west than the ECMWF. This difference is impacting timing details on a shallow moisture boundary associated with an old front moving through the state Friday night and Saturday. Given the timing uncertainty, we will continue to advertise a typical trade wind weather pattern, with the expectation that a 6-12 hour period could be rather wet when this boundary moves through. Beyond that, fairly typical trade wind weather can be expected Saturday night through the middle of next week, with showers favoring windward and mauka areas and a few showers spilling leeward from time to time.

Aviation

Moderate trades will continue, with clouds and light showers favoring windward and mauka locations. MVFR CIGs/VSBYs will persist this morning for some windward areas, mainly in showers. Some of these showers are managing to spread into leeward sections of the smaller islands.
AIRMET Sierra is now in effect for mountain obscuration over north through southeast facing slopes of Kauai, and will likely continue through the morning hours today. Other windward locations may need to be included later this morning.

Marine

Fresh easterly trades develop tonight into Friday as high pressure builds over the islands in tandem with deepening low pressure northwest of the area. The Small Craft Advisory remains posted for the typical windier waters and will likely require expansion as winds continue strengthening into the weekend. Fresh trades continue well into next week.
The current moderate, long period NW swell peaked yesterday evening into last night and will now steadily subside through the remainder of the week. Another moderate, long period NW (330) swell is modeled to arrive early this weekend bringing similar surf to exposed shorelines. Surf may approach the advisory threshold during its peak late Saturday into Saturday night.
East-facing shores remain dominated by short period wind wave through the near term. However, deep low pressure descending from the Gulf of Alaska down the West Coast of the mainland US will generate a moderate, medium period NNE (060) swell that will fill in late this weekend and peak early next week.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov