West Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 68 to 73 near the shore to around 60 above 3000 feet. Northeast winds 10 to 20 mph shifting to the east up to 20 mph after midnight. Chance of rain 50 percent.

Monday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 85 near the shore to around 72 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy with scattered showers. Lows 67 to 72 near the shore to around 59 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 71. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Monday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 78 to 86. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 71. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 62 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 79 in the valleys to around 62 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Monday Night: Breezy. Mostly cloudy with numerous showers. Lows 61 to 68 in the valleys to around 57 above 4000 feet. East winds 15 to 25 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 63 to 72. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 73 to 84. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Monday Night: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 72. East winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 63 to 75. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 83. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Monday Night: Breezy. Mostly cloudy with numerous showers. Lows 63 to 75. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A weakening frontal boundary will continue to move south across the Big Island tonight. Breezy to locally strong trades will persist through much of the week, becoming even stronger by mid- week as strong high pressure builds north of the islands. Typical windward and mauka showers will prevail, with generally drier conditions over leeward areas.

Discussion

Radar and satellite imagery show a weakening frontal boundary draped across the Big Island this afternoon. Clouds and light to brief moderate showers remain focused over windward and mauka areas of Oahu, Molokai, Maui, and the Big Island, with the occasional spillover into leeward areas of the smaller islands. Rainfall totals over the last 6 to 12 hours ranged from 0.20 inches over portions of windward Oahu to over 4 inches along portions of windward Molokai and Maui. Portions of windward Big Island have already received close to 2 inches of rain today.
Guidance continues to show a diffuse frontal boundary moving south across the rest of the Big Island tonight. This will bring some much needed rainfall to portions of the Kau District, but mid- level ridging will continue to limit vertical development. Expect slightly drier and more stable conditions to continue post- frontal as high pressure builds north of the state. This slightly drier air mass will bring lower dew points to the area so temperatures will feel cooler than normal over the next couple of days.
Aside from some light and variable winds over portions of southeast Big Island this afternoon, recent obs and the latest ASCAT pass shows breezy to locally strong northeast winds have filled in across much of the state. Expect wind speeds to slowly strengthen over the next couple of days and peak mid-week as strong high pressure builds far north of the state. Based on the latest guidance a wind advisory may be necessary for portions of the state later this week. Otherwise, windy trades continue through much of the week with clouds and showers favoring windward and mauka areas under stable conditions.

Aviation

A weakening front, currently near the Big Island, will continue to sag southward through tonight. Enhanced showers and MVFR conditions will accompany this boundary, with breezy NE winds now over most of the state behind it. VFR conditions will prevail behind the front, but MVFR conditions are still likely along windward higher terrain as moisture and showers continue to ride in and bank up against the mountains. NE winds are expected to strengthen further over the next couple of days after the front moves out.
AIRMET Sierra remains in effect for N thru E sections of Oahu through the Big Island for MTN obscurations due to low clouds and showers from the front. Additional areas may be dropped from this AIRMET as conditions improve behind the front.
AIRMET Tango remains in effect for low-level turbulence over and downwind of island terrain across the entire state as winds strengthen behind the front.
In addition, due to the ongoing eruption of Kilauea today, SIGMET Tango is currently in effect over and southwest of the volcano for a mixture of volcanic ash and gas emissions extending up to FL150. this SIGMET will be updated or cancelled as additional information becomes available.

Marine

Weakening remnants of the old cold front is near the Big Island waters this afternoon and will continue to push southeast through tonight. In its wake, fresh to strong northeast trade winds will fill in and maintain over all marine zones. A Small Craft Advisory has been expanded and extended through Monday night for all coastal marine zones due to a combination of winds and high seas. High pressure north of the waters looks to strengthen and build Wednesday and Thursday increasing the trade winds to near-gale force speeds over the windier waters and channels around Maui County and the Big Island.
The current moderate medium period north-northwest swell is expected to fade slightly through the evening hours before a moderate to large north- northeast swell is expected to fill in late tonight. Offshore NDBC buoy 51001 to the northwest as well as buoy 51000 to the north have shown signs of this swell this afternoon. Due to the 11 to 13 second period, swell energy from the north-northeast is expected to reach shorelines late tonight into Monday morning and hold through Monday night. A High Surf Advisory (HSA) has been issued for north facing shores starting at midnight through Tuesday morning. A Marine Weather Statement (MWS) coinciding with the north- northeast swell has also been issued for all windward waters starting at midnight through Tuesday morning due to the potential for surges in north facing harbors including Hilo and Kahului. The MWS may need to be extended through the middle of the week but will be determined at a later time.
Later this week, a moderate northwest swell is expected to fill in late Tuesday, and peak Wednesday near High Surf Advisory levels for north and potentially west facing shores. Also, a northeast swell from a forming low pressure system to the northeast is expected to be mixed in with the rough choppy seas from the trade winds.
East facing shores will exhibit large rough choppy seas through the forecast period, with potentially the largest surf at High Surf Advisory levels during the middle of the week.
A small, long period, south-southwest swell will keep surf heights near seasonal averages along south facing shores through this evening. A series of south swells is expected Monday through Thursday which will keep surf elevated.

Fire weather

Critical fire weather conditions not expected the next couple of days. Breezy to locally strong trades will continue across the state through much of the week, but low-level moisture embedded within the trades should help to keep relative humidity from reaching critical thresholds.

HFO Watches/Warnings/Advisories

High Surf Advisory from midnight tonight to 6 AM HST Tuesday for Niihau, Oahu North Shore, Olomana, Maui Windward West, Kauai North, Kauai East, East Honolulu, Koolau Windward, Molokai Windward, Molokai Southeast, Molokai North, Maui Central Valley North, Windward Haleakala, Kipahulu, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Tuesday for all Hawaiian waters,