Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny with scattered showers in the morning, then cloudy with showers in the afternoon. Highs around 82 near the shore to around 67 above 3000 feet. Northwest winds up to 10 mph. Chance of rain 80 percent.

Tonight: Cloudy with showers. Lows around 69 near the shore to around 59 above 3000 feet. Southeast winds around 10 mph. Chance of rain 80 percent.

Friday: Showers and isolated thunderstorms. Highs around 83 near the shore to around 69 above 3000 feet. South winds 10 to 15 mph. Chance of rain near 100 percent.

South Kaua’i

Today: Partly sunny with scattered showers in the morning, then cloudy with showers in the afternoon. Highs 76 to 82. West winds around 10 mph shifting to the southwest in the afternoon. Chance of rain 80 percent.

Tonight: Cloudy with showers. Lows around 68. South winds around 10 mph. Chance of rain 80 percent.

Friday: Showers and isolated thunderstorms. Highs 75 to 83. South winds 10 to 15 mph. Chance of rain near 100 percent.

Kaua’i Mountains

Today: Mostly cloudy with numerous showers. Highs 70 to 77 in the valleys to around 62 above 4000 feet. Light winds becoming northwest around 10 mph in the afternoon. Chance of rain 70 percent.

Tonight: Cloudy with showers. Lows around 66 in the valleys to around 57 above 4000 feet. South winds 10 to 15 mph. Chance of rain 90 percent.

Friday: Breezy. Showers and isolated thunderstorms. Highs 70 to 81 in the valleys to around 62 above 4000 feet. South winds 10 to 20 mph. Chance of rain near 100 percent.

North Kaua’i

Today: Mostly cloudy with numerous showers. Highs 71 to 82. North winds up to 10 mph. Chance of rain 70 percent.

Tonight: Cloudy. Numerous showers in the evening, then showers after midnight. Lows 63 to 71. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 80 percent.

Friday: Showers and isolated thunderstorms. Highs 74 to 85. South winds up to 10 mph. Chance of rain near 100 percent.

East Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 70 to 81. West winds up to 10 mph shifting to the south around 10 mph in the afternoon. Chance of rain 70 percent.

Tonight: Cloudy with showers. Lows 64 to 72. South winds around 10 mph. Chance of rain 90 percent.

Friday: Showers and isolated thunderstorms. Highs 70 to 82. South winds 10 to 15 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

Southerly kona winds will continue pulling up unstable tropical moisture from the deep tropics over the next few days. A kona low remains in place roughly 600 miles north to northwest of the Hawaiian Islands as a weakening low level trough begins to move into Kauai. Bands of showers producing moderate to heavy rain and thunderstorms will develop in this tropical air mass and affect most islands through Friday. The kona low will begin to drift away from the state this weekend with improving trends over the western islands into the upcoming weekend. By Monday all islands will see a dramatic improvement in weather conditions as easterly trade winds return.

Discussion

In the larger scale, satellite imagery this morning shows a kona low system roughly 600 miles north to northwest of the Hawaiian Islands with a weakening trough moving into the islands of Kauai and Niihau from the northwest. Southerly winds ahead of this system continues to pull up deep unstable tropical moisture over the islands. A combination of local radar and satellite imagery show convective shower bands moving into most of the islands from the south. These shower bands will produce periods of moderate to heavy rain across much of the state through Friday. Soil moisture levels remains saturated for most areas, which means any additional heavy rainfall could swiftly turn into runoff and a threat for flash flooding. For these reasons a Flood Watch remains in effect for most of the state. The flood threat for the Big Island remains at a lower threat level, therefore the Big Island is not in the watch at this time.
Kauai County and Oahu weather impacts…The low level trough moving into Kauai County this morning will combine forces with the unstable tropical air mass over the next few days. Increasing low level surface convergence with upper lift from a 500 mb trough passing over the islands will help to lift the unstable moisture over the mountain slopes of Kauai and Oahu, increasing the threat for flooding due to moderate to heavy showers and thunderstorms potentially training over the island. The medium range forecast guidance show drier and more stable east to southeasterly winds as the ridge builds in from the east and the kona low drifts northward from Friday night into Saturday morning. Any delay in the ridge building back in will slow down these improving weather trends this weekend.
Maui County weather impacts…Deep tropical moisture in southerly kona winds periods of moderate to heavy showers over the islands of Maui County over the next few days. The main threats for Maui County will be if several storms line up over any one location potentially producing 1 to 2 inches per hour rainfall for several hours. These small scale convective shower bands are notoriously hard to predict well in advance. These areas affected by this flood threat may often see fair conditions that rapidly deteriorate into heavy rain with rapid runoff and flooding in a very short time period.
Big Island weather impacts…Tropical moisture will affect the Big Island into Friday. The southeastern slopes of the Big Island would be in the highest threat level for moderate to heavy rain during this event. Most of the deep convective showers should remain west of the Big Island this week with just a slight risk of flooding over Hawaii County.
Saturday through Monday…We gradually transition back to a drier weather pattern as high pressure builds in from the east producing a drier and more stable southeasterly wind flow pattern across the Hawaii region as the kona low drift farther northward away from the state. Easterly trade winds should return by Monday.

Aviation

A strong kona low about 650 nm northwest of Kauai is pulling tropical moisture out of the south southeast across the state. This will keep the Hawaiian Islands in an active weather pattern through the remainder of the week. Moderate to heavy showers and possible thunderstorms are expected over the central islands today and tomorrow. On the Big Island, enhanced shower activity is expected in the afternoon and early evening hours.
Latest radar imagery reveals a broad band of intensifying showers and thunderstorms streaming across Oahu and the Kaiwi Channel. This band is expected to shift eastward today, spreading across the whole of Maui county by late this evening.
AIRMET Sierra is in effect for Kauai and Oahu for mountain obscuration. Conditions will likely spread across Molokai and Lanai by midmorning. Occasional IFR conditions could develop over Kauai after sunrise.
AIRMET Tango is in effect for mechanical turbulence below 120 kft N thru E of the Big Island. Conditions could spread to East Maui later today as the gradient aloft tightens.

Marine

Fresh to locally strong south to southeast winds associated with a kona low north-northwest of the state will persist through Friday for most waters. A shift out of the east to southeast direction is expected over the weekend through early next week as it lifts northward and away from the area. A Small Craft Advisory has been issued for the Windward and Leeward Big Island waters (Hamakua Coast and waters near South Point). In addition to the winds, expect locally rough seas in heavy showers or storms that develop over the next few days, with the best chances being over the waters west of Maui County. Seas should remain just below the advisory level over the exposed Kauai waters as a short-period northwest swell moves through (peaking today through tonight).
Surf along south facing shores will remain up through early next week due to overlapping, long-period south-southwest swells expected. The first will rise through the day today, then peak tonight through Friday, likely reaching the advisory level. Offshore buoys 51003 and 51004 (51002 remains down) reflect this with the peak energy coming in within the 19 and 21+ second bands. As a result, a High Surf Advisory has been issued through Friday. Expect rough conditions for most southerly exposures through this period due to a combination of the onshore winds, swell, and periodic heavy showers moving through. As this swell slowly eases over the weekend, a fresh, long-period south- southwest swell will begin to fill in through the day Sunday. This will peak early next week before easing through midweek.
Surf along north and west facing shores has trended up overnight on Kauai, with observations coming in larger than expected. Given the energy being spread over the short-period bands, heights should remain below the advisory thresholds for north and west facing shores. Expect a similar trend over exposed waters down the island chain today as it continues to build. This will linger into Friday, then ease through the weekend.
Surf along east facing shores will remain well below average through the weekend. An upward trend is possible next week as the trades return locally and far upstream over the eastern Pacific.

HFO Watches/Warnings/Advisories

Flood Watch through Friday evening for Kauai, Niihau, Oahu, Molokai, Lanai and Maui.
High Surf Advisory until 6 PM HST Friday for south facing shores of all islands.
Small Craft Advisory until 6 PM HST Friday for Big Island Windward Waters, Big Island Leeward Waters.

Data Courtesy of NOAA.gov