Hilo

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 63 to 69 near the shore to 49 to 56 at 4000 feet. North winds up to 15 mph shifting to the west after midnight. Chance of rain 20 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 78 to 83 near the shore to 63 to 68 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 63 to 69 near the shore to 49 to 56 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 72 near the shore to 46 to 51 near 5000 feet. Light winds. Chance of rain 50 percent.

Thursday: Partly sunny. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 83 to 89 near the shore to around 66 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 72 near the shore to 47 to 52 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Tonight: Breezy. Partly cloudy with isolated showers. Lows 62 to 71 near the shore to 52 to 61 near 3000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Thursday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 80 near the shore to 70 to 79 near 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Thursday Night: Breezy. Mostly clear with isolated showers. Lows 61 to 70 near the shore to 53 to 61 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Kohala

Tonight: Breezy. Partly cloudy with isolated showers. Lows 62 to 71 near the shore to 52 to 61 near 3000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Thursday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 80 near the shore to 70 to 79 near 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Thursday Night: Breezy. Mostly clear with isolated showers. Lows 61 to 70 near the shore to 53 to 61 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

South Big Island

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening. Lows around 73 near the shore to around 50 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Thursday: Breezy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 87 near the shore to around 66 near 5000 feet. East winds up to 25 mph. Chance of rain 50 percent.

Thursday Night: Mostly clear. Breezy. Isolated showers in the evening. Lows around 73 near the shore to around 51 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 63 to 69 near the shore to 49 to 56 at 4000 feet. North winds up to 15 mph shifting to the west after midnight. Chance of rain 20 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 78 to 83 near the shore to 63 to 68 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 63 to 69 near the shore to 49 to 56 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Partly cloudy. Isolated showers in the evening. Lows 70 to 75 near the shore to 49 to 54 above 4000 feet. Northeast winds up to 15 mph shifting to the southeast after midnight. Gusts up to 35 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Breezy. Scattered showers and isolated thunderstorms in the afternoon. Highs 82 to 90 near the shore to 64 to 71 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 50 percent.

Thursday Night: Mostly clear. Isolated showers in the evening. Lows 70 to 75 near the shore to 49 to 55 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

High pressure will meander around far northwest of Hawaii through Saturday, keeping breezy trades blowing. A low aloft approaching the islands from the north will enhance incoming trade wind showers starting tonight, and continuing through Friday. A few downpours are possible, and a rumble or two of thunder can't be ruled out, mainly for Kauai and Oahu which will be closest to the upper low. The holiday weekend will see us trend to much drier and more settled tradewind weather as the upper low moves away.

Discussion

Breezy trade winds over the islands are being driven by a relatively strong and large high, shown on scatterometer data roughly 1200 mi NNW of Kauai. Models show this high will meander around the same general area through Sat. Meanwhile, a mid- to upper- level low located about 350 miles NNW of Kauai is pushing SSW. Global models are in good agreement that this low will settle in near or over the main Hawaiian Islands on Thu.
The low will be accompanied by fairly impressive cold air aloft, with 500 mb temperatures over Kauai expected to drop to about 2-sigma below normal Thu morning. Guidance thus shows about 1000-1500 J/kg of 500 m MLCAPE, along with a small pocket of upper level divergence over the northern main islands. However, at the same time, models insist that trades will continue in the boundary layer with bands of low-level moisture riding through from time to time, with one of those noteworthy bands arriving Fri.
This setup will help to enhance incoming bands of clouds and showers riding in on the trades, and might even lead to a couple of brief thundershowers as well (a pattern sometimes colloquially known as “thundertrades”). The latest NBM thunder guidance maxes out below 10 percent near Niihau Thu night, then fades quickly. However, our locally developed hekili guidance shows probabilities from 10-20 percent over and around Kauai and Oahu from both GFS and ECMWF, lingering into Friday before dropping as the upper low starts to move away to the NE. Usually in patterns like this, the most favorable areas for thunder are in the ribbons of low-level convergence downwind of the islands, but it's not impossible to get hefty downpours and a rumble or two windward and mauka too as trade wind shower areas move in from the ENE. Based on a blend of this data and pattern recognition, will keep a mention of t-showers in the forecast for portions of Kauai and Oahu tonight through Fri. Interior Big Island will also continue to have a small chance for a couple of upslope thundershowers Thu afternoon, just like we saw today over the south flank of Mauna Loa where NLDN detected a single lightning strike there.
The southern end of the chain should not see as much shower enhancement from the rather compact upper low, but trades will still be somewhat wet from time to time due to the proximity of the upper low, as any more organized pockets of moisture ride in.
The airmass stabilizes by the holiday weekend as the upper low moves quickly away. Wet trades will become much drier, with fewer clouds and showers, and more sunshine. Trade wind speeds will eventually ease some as the high to the N weakens to a much weaker subtropical ridge by the middle of next week.

Aviation

Moderate to locally breezy trade winds will strengthen slightly heading into tomorrow. Low clouds and showers will favor windward and mauka areas, particularly overnight and during the morning hours, with showers reaching leeward communities at times. MVFR conditions will be possible in showers. Otherwise, VFR conditions will prevail.
No AIRMETs are in effect this afternoon. AIRMET Sierra might be needed for mountain obscuration across windward areas overnight into tomorrow morning as shower coverage is expected to increase.

Marine

High pressure to the distant north- northwest will maintain moderate to locally strong trade winds through the weekend. An upper level low to the north of the waters may bring periods of instability and isolated thunderstorms over Kauai and portions of Oahu waters tonight through Thursday. A Small Craft Advisory is in effect for the windier waters and channels around Maui County and the Big Island through Thursday and may need to be extended through the weekend.
Surf along south facing shores will remain small to moderate as a long period south-southwest swell is expected to fill in late tonight into Thursday. A second pulse from the same direction will fill in over the weekend and keep small to moderate surf through the weekend before declining early next week.
East shore surf will remain near seasonal average during the next couple of days as trade winds persist. Tiny surf will prevail along north facing shores this week and into the weekend.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov