Hilo

Tonight: Mostly cloudy with numerous showers. Locally heavy rainfall possible in the evening. Lows 68 to 76 near the shore to around 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Monday: Partly sunny with scattered showers. Highs 81 to 88 near the shore to 67 to 74 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 67 to 75 near the shore to 57 to 62 at 4000 feet. North winds up to 10 mph. Chance of rain 50 percent.

Kona

Tonight: Partly cloudy. Scattered showers in the evening. Lows 70 to 77 near the shore to 54 to 59 near 5000 feet. Light winds. Chance of rain 40 percent.

Monday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 86 to 91 near the shore to around 72 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows 69 to 76 near the shore to 54 to 59 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 68 to 75 near the shore to 63 to 69 near 3000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 83 near the shore to 71 to 82 near 3000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 67 to 75 near the shore to 61 to 69 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 68 to 75 near the shore to 63 to 69 near 3000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 83 near the shore to 71 to 82 near 3000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 67 to 75 near the shore to 61 to 69 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Partly cloudy. Breezy. Scattered showers in the evening. Lows around 77 near the shore to around 60 near 5000 feet. East winds up to 20 mph. Chance of rain 30 percent.

Monday: Breezy. Mostly sunny with isolated showers. Highs around 88 near the shore to around 71 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Lows around 76 near the shore to around 60 near 5000 feet. East winds up to 15 mph shifting to the northeast after midnight.

Puna

Tonight: Mostly cloudy with numerous showers. Locally heavy rainfall possible in the evening. Lows 68 to 76 near the shore to around 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Monday: Partly sunny with scattered showers. Highs 81 to 88 near the shore to 67 to 74 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 67 to 75 near the shore to 57 to 62 at 4000 feet. North winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Partly cloudy. Isolated showers in the evening. Lows 72 to 77 near the shore to 56 to 61 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs 85 to 92 near the shore to 68 to 76 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Monday Night: Mostly clear. Lows 72 to 77 near the shore to 55 to 60 above 4000 feet. East winds up to 10 mph.

Detailed Forecast

Synopsis

Trades continue with breezy winds through Monday before weakening slightly Tuesday, then strengthening again Wednesday through Friday. Moisture will decrease late Monday, leading to relatively dry trades from then until late in the week. There is a significant potential (90% chance) for a tropical system to form to our ESE soon. It is expected to head in the general direction of Hawaii, but we don't yet know how close it may come. Everyone is advised to stay informed as new forecasts are issued.

Discussion

Radar indicates some moderate to strong showers on the Big Island, where conditions are favorable for weak thunderstorms to form (no lightning has been observed as of 3:30 PM HST). Elsewhere, light showers were seen mainly across windward and mauka areas of Maui County, with little to no shower activity over the Island of Oahu or Kauai County.
A strong upper level high to our northeast will help keep trades going through the coming work week. The high is forecast to retrograde westward late in the week, and this will a significant factor in the track of the potential tropical storm currently expected to form to our ESE and then move WNW. The area is currently known as Invest 93C, and NHC confidence is high (90%) that what will eventually be named Lala will form soon. Model spread is also high, with some solutions taking the system north of the islands, some south, and a few going through our state. No official forecast exists yet. It will take another day or two before we have a forecast track. At this point, we suggest that folks make sure they are prepared and make sure to stay informed. NHC will handle the track forecast. We will handle local impacts, if any, and we are still some time away from knowing what those might be.

Aviation

Fresh trades expected for the next several days. AIRMET Tango is in effect for tempo moderate turbulence downwind of island terrain due to wind speeds.
AIRMET Sierra is posted for mountain obscurations above 2500 feet for windward sides of Oahu, Molokai, Maui and Big Island due to a steady stream of showers carrying in with the trade winds.

Marine

High pressure to the far northeast will remain nearly stationary through midweek as moderate to locally strong trade winds will persist through Wednesday. A Small Craft Advisory (SCA) is in effect through Monday afternoon for the windier waters and channels around Maui County and the Big Island. Borderline conditions will likely continue through at least Wednesday, which may prompt further extensions of the SCA. Later in the week, the focus will shift to the deep tropics southeast of the state. Latest guidance from the National Hurricane Center has a high chance in 7 days for a tropical storm to form southeast of the islands. Depending on the track, it will have differing effects on local winds, seas and weather as early as Thursday.
Surf along south facing shores will remain near the August average through Monday as overlapping south swells impact the islands. Surf looks to slowly building through the week. A larger moderate long period south swell is expected to fill in Wednesday and remain elevated through Friday prompting the potential for a High Surf Advisory at its peak.
Surf along east facing shores will continue to remain moderate and rough due to moderate to locally strong trade winds. Later in the week, the potential of the developing tropical's track will dictate the potential for a swell from the southeast to east. Aside from wrapping trade wind energy, surf along north-facing shores will remain flat to tiny through the week.
Due to a combination of peak monthly high tides and water levels running higher than predicted in a few locations, a Coastal Flood Statement is in effect for minor coastal flooding possible around the afternoon high tide through at least Tuesday. Tides will be decreasing on Wednesday, but coastal flooding may continue to be possible around high tide for locations where water levels are running highest.

Fire weather

Moderate fire weather conditions are expected for Kauai and Oahu through Monday under light to breezy trade winds and trade wind showers. Fire weather concerns will be lower over Maui County and the Big Island, where higher rain amounts are forecast through Monday morning.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov