Photo Credit: Brendan Stephen

West Kaua’i

Rest Of Today: Mostly cloudy. Isolated showers in the morning, then numerous showers in the afternoon. Highs around 87 near the shore to around 75 above 3000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 72 near the shore to around 62 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs around 88 near the shore to around 74 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Rest Of Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 79 to 87. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 79 to 88. East winds 10 to 15 mph. Chance of rain 80 percent.

Kaua’i Mountains

Rest Of Today: Mostly cloudy. Numerous showers in the morning, then occasional showers in the afternoon. Highs 74 to 84 in the valleys to around 64 above 4000 feet. East winds 10 to 15 mph. Chance of rain 80 percent.

Tonight: Numerous showers in the evening, then occasional showers after midnight. Lows 64 to 71 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

Monday: Breezy. Mostly cloudy with occasional showers. Highs 73 to 84 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

North Kaua’i

Rest Of Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 76 to 88. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows 66 to 73. East winds up to 15 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 75 to 88. East winds up to 15 mph. Chance of rain 80 percent.

East Kaua’i

Rest Of Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 72 to 85. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Numerous showers in the evening, then occasional showers after midnight. Lows 66 to 76. East winds up to 15 mph. Chance of rain near 100 percent.

Monday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 71 to 85. East winds 10 to 15 mph. Chance of rain 80 percent.

Detailed Forecast

Synopsis

A statewide Flood Watch remains in effect through the day. Widely scattered showers, with occasional periods of heavy rain and isolated thunder, will likely occur through this evening. A drier, more typical breezy trade wind pattern will return from Monday onward.

Discussion

An upper level low from the north will be moving over the islands today. This low aloft will provide enough instability within a very moist resident air mass to justify a high probability of continued moderate to occasional bouts of heavy rain over the majority of the islands. The heaviest rain is occurring over eastern Maui this morning where it will not take much more rain to exacerbate flooding issues downslope of the Hanawi and Hana Reserves. Radar estimates of between 6 to 12 inches of rain have fallen over eastern Maui the past 36 hours. Due to very saturated grounds across both Oahu and Maui, relatively lower rainfall rates could initiate flooding across these islands.
Very little synoptic scale change to this unstable scenario warrants a higher awareness of return periods of moderate to strong rain intensity/rates that could persist into late evening. While instability indices remain low, the presence of the upper low within this saturated column (unseasonably high near 2.00 inch precipitable waters) will keep this mention of isolated thunder and localized heavy rain in place. Deep moisture with enhanced large scale lift brought on by the upper level low will keep the all-island Flood Watch in effect until 6 PM HST.
Trades will become locally breezy as ridging builds in northeast of the state the next couple of days. This will reinstate a tighter upstream pressure gradient and restrengthen trades. This wind pattern will focus the highest, most intense precipitation over windward mauka slopes. Wind sheltered leeward areas, such as the Kona slopes of Big Island, hold higher odds of getting into the intense rainfall action with possible isolated thunder today, especially if there are early day cloud breaks providing peeks of sun. As the upper low washes out southwest of the islands and surface ridging builds to the north into Tuesday, a breezy and increasingly stable trade wind regime is expected from Monday onward. Pockets of higher mid-level moisture riding in on trades will contribute to intermittent windward-exposed shower activity throughout next week. It appears the highest rainfall from a slug of passing mid layer moisture will likely drop the greatest areawide rainfall Thursday and/or Friday.

Aviation

The potential for heavy showers and thunderstorms will remain in the forecast as a broad upper low lingers over the region. Although the best chance for this activity will occur over windward and mauka locations with breezy trades returning today, some will manage to spill over or develop across leeward locations. Expect mountain obscurations above 2000 feet periodically for most windward locations today, especially over the eastern end of the state.
AIRMET Tango is posted for moderate turbulence between FL250 and FL450). Low-level turbulence downstream of island terrain is possible later today.
Light icing is possible between 120 and FL200 this morning due to thick layered mid-level clouds streaming from west to east over the eastern end of the state.

Marine

High pressure will build far northeast of the islands over the next couple of days as a front between the islands and the high gradually dissipates. Trade wind speeds will increase through today and remain fresh to locally strong for the next several days, primarily in response to the strengthening high, A Small Craft Advisory (SCA) remains in effect for waters around Maui County and the Big Island. A disturbance aloft will increase potential for heavy showers and thunderstorms today.
A medium period northeast swell will continue to decline for at least the next several days. However, the combination of strengthening trades and a small long period east swell from Tropical Cyclone Kristy may produce elevated surf along east facing shores for most of the new week. A small to moderate medium period north swell should arrive today and peak Monday, then gradually decline. A long period south swell will slowly decline over the next couple of days. A long period northwest swell arrive may arrive by Friday.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov