Hilo

Today: Partly sunny with scattered showers. Highs 80 to 87 near the shore to around 68 at 4000 feet. Northeast winds up to 15 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 51 to 58 at 4000 feet. East winds up to 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Thursday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 81 to 88 near the shore to around 69 at 4000 feet. Southeast winds up to 10 mph shifting to the east around 10 mph in the afternoon. Chance of rain 20 percent.

Kona

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 84 to 89 near the shore to around 70 near 5000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy after midnight. Lows around 74 near the shore to 50 to 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Thursday: Partly sunny. Highs around 87 near the shore to around 70 near 5000 feet. Light winds.

Waimea

Today: Breezy. Mostly sunny with isolated showers. Highs 65 to 87. East winds up to 20 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 64 to 73 near the shore to 55 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning. Highs around 82 near the shore to 71 to 81 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Kohala

Today: Breezy. Mostly sunny with isolated showers. Highs 65 to 87. East winds up to 20 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 64 to 73 near the shore to 55 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning. Highs around 82 near the shore to 71 to 81 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Big Island

Today: Mostly sunny. Breezy. Scattered showers in the afternoon. Highs around 87 near the shore to around 69 near 5000 feet. East winds up to 25 mph. Chance of rain 40 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Lows around 75 near the shore to around 56 near 5000 feet. East winds 10 to 20 mph.

Thursday: Partly sunny in the morning then becoming mostly sunny. Breezy. Highs around 88 near the shore to around 69 near 5000 feet. East winds 10 to 20 mph.

Puna

Today: Partly sunny with scattered showers. Highs 80 to 87 near the shore to around 68 at 4000 feet. Northeast winds up to 15 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 51 to 58 at 4000 feet. East winds up to 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Thursday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 81 to 88 near the shore to around 69 at 4000 feet. Southeast winds up to 10 mph shifting to the east around 10 mph in the afternoon. Chance of rain 20 percent.

Waikoloa

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 88 near the shore to 67 to 76 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Gusts up to 40 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows around 75 near the shore to 52 to 57 above 4000 feet. Light winds.

Thursday: Mostly sunny. Highs 85 to 90 near the shore to 67 to 76 above 4000 feet. East winds up to 10 mph shifting to the northwest around 10 mph in the afternoon.

Detailed Forecast

Synopsis

A stable and relatively dry pattern will persist through Thursday, along with moderate to locally breezy trade winds, bringing limited clouds and showers to windward and mauka areas. Increased shower activity is expected Thursday night into the weekend. A return to a more stable trade wind pattern is expected early next week.

Discussion

No substantial changes to the forecast with the morning forecast package. Some clouds and showers are riding in on the trades, focusing activity to the windward and mauka sections of the smaller islands. Another areas of clouds and showers upstream of the Big Island will move onshore later this morning.
High pressure is expected to remain north of the islands into the weekend, so expect trade winds to remain in place. However, a decaying surface trough far east of the islands and the tail end of a weakening front draped roughly along 30 to 35N will be pinched off beneath the strengthening high pressure. The moisture from these features will then be carried in on the trade winds to the islands. The ECMWF and GFS continue to agree with precipitable water (PW) values reaching 2 inches near the islands, which is well above average for September.
At the same time, a mid- to upper-level low is forecast to set up near Kauai, bringing 500 mb temperatures down to around -8 to -9 C which is also colder than normal for September. Forecast soundings show the trade inversion lifting to near 10 kft or higher as deeper moisture arrives. Despite the lack of a significant surface feature, those PW and 500 mb temperatures could very well spark some thunderstorm activity, and there is the chance for locally heavier showers. Based on the global models, the main focus for this would be the western half of the state Friday into Saturday. Any heavier cells should remain fast moving within the persistent trades, limiting the duration of heavy rainfall at any one location.
Thunderstorms have not yet been added to the forecast as we await to see some of these model depictions start to appear in the observed data.
Showers will gradually diminish late Sunday into early next week as upper ridging reestablishes and drier air filters back across the islands.

Aviation

Locally breezy trade winds will continue through the period. Some clouds and showers riding in on the trade winds will favor windward and mauka areas. VFR conditions are expected to prevail with pockets of MVFR within passing showers.
No AIRMETs currently in effect, and not anticipating any to be issued today.

Marine

Surface high pressure will remain anchored north of the state for the next several days and bring moderate to locally strong trade winds across the waters. However, winds are set to decrease slightly by Friday as a front drops south and weakens the high. The latest ASCAT pass depicted winds meeting Small Craft Advisory thresholds over portions of the western waters. To account for this, Small Craft Advisories have been issued for the Kauai Channel and Kauai leeward waters in addition to the typically windy areas around Maui County and the Big Island. These advisories will likely be scaled back to the just the typical windy areas from Thursday onward.
Surf along south facing shores will be tiny to small over the next few days with mainly background south and southeast energy. A small to moderate, long-period, south southwest swell will build Saturday into Sunday and help boost south shore surf heights back up to near or above the September average.
Surf along north facing shores should see a small increase late today into tomorrow as a short period northerly swell fills in. This small bump is expected to peak on Friday out of the north to north- northeast direction, followed by a short period north northwest swell this weekend. Moderate to locally strong trades near and upstream of the area will lead to slightly elevated and choppy conditions along east facing shores through this weekend.

Fire weather

Expect decreasing fire weather risk as humidity gradually increases through the week and into the weekend. Rain chances will increase Thursday night into the weekend as deep pockets of moisture filter in on the trades, helping to potentially further alleviate fire weather concerns. Sustained winds briefly hover near to below the critical fire weather threshold each afternoon through Thursday, then trend slightly lighter for the weekend.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Thursday for Kauai Leeward Waters, Kauai Channel.
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