Photo Credit: Jason Weingardt

West Kaua’i

Today: Partly sunny with scattered showers. Highs around 84 near the shore to around 69 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to around 58 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs around 84 near the shore to around 69 above 3000 feet. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny with scattered showers. Highs 76 to 83. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 68. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 77 to 83. Northeast winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 81 in the valleys to around 61 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 66 in the valleys to around 56 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy with numerous showers. Highs 71 to 80 in the valleys to 59 to 64 above 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 83. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 71. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 74 to 84. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 81. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 72. Northeast winds around 10 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy with numerous showers. Highs 71 to 82. Northeast winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A low pressure system moving into the Central Pacific basin north of Hawaii will weaken the subtropical ridge and keep light to moderate trade winds in the forecast this week. An unstable environment will enhance shower activity across the Hawaii region through the weekend with the highest rainfall amounts favoring the windward and mountain areas. The potential for slow moving heavy showers and thunderstorms are growing from Friday into the weekend as a developing upper level low stalls out over the islands.

Discussion

Weak upper level troughing will continue to enhance trade wind showers today. A low level cloud band, the remnants of an old East Pacific cold front, will drift through the islands on Thursday as an upper level trough digs into the Hawaii region from the north. A combination of the low level cloud band and upper level forcing from the upper trough will produce increasing wet weather trends across the state from Thursday onward.
A weakening subtropical ridge north of the islands this week will keep light to moderate trade winds in the forecast through at least Sunday. Stronger winds aloft are creating warning level wind speeds over the Big Island summits of Mauna Loa and Mauna Kea this morning, these strong winds may continue above advisory levels through tonight. A High Wind Warning was issued this morning for the highest summits on the Big Island. Elsewhere in the lower elevation areas, a hybrid sea breeze and trade wind pattern will develop along terrain sheltered leeward areas. The wind pattern changes again by this weekend, as an upper level low sets up directly over the islands producing a surface trough reflection over the islands and light to moderate east to southeasterly winds.
A rather unstable weather pattern develops over the Hawaiian Islands in the latest model guidance from Friday through Sunday as the upper low deepens and stalls over the state. This pattern change may bring the potential for slow moving heavy rain showers and thunderstorms over some islands in the state. The heavy rain and thunderstorm impacts with this upper low will vary greatly depending upon the precise location where the low center sets up relative to each island. If the upper low moves in north and west of the island chain then the northwest islands of Kauai and Oahu would be under a higher rainfall threat levels. If the upper low sets up more over the south and east section of the state, then Maui County and the Big Island will see higher threats for heavy rain and thunderstorms. Rainfall coverage was increased and isolated thunderstorms were added to the forecast for this end of this week to account for more consistency in the run to run medium range forecast guidance. The threat for flash flooding over all islands is growing with time, however it remains too early to pin down the highest flood threat areas with a Flood Watch product.
More island by island impacts will be revealed as the forecast time period grows shorter, and the upper low track with weather impacts evolve over time. Stay tuned.

Aviation

Moderate trade winds will prevail across the island chain today, then ease up a bit tonight especially over the western islands. Low clouds and showers will continue to favor windward and mauka areas, with MVFR cigs/vsbys possible as showers move through. A stray shower may spill leeward at times, but predominantly VFR conditions are expected here.
AIRMET Sierra remains in effect for windward sections of Kauai and Oahu. Conditions should improve here later this morning.

Marine

Fresh to strong trade winds will slowly ease through Wednesday as a 1030 mb high 1000 nm north northeast of the islands moves off to the northeast. A Small Craft Advisory (SCA) remains in effect for the typically windy waters around the Big Island and Maui County through this afternoon and continues to look like it may be dropped by this evening as winds ease to moderate to locally fresh. A surface trough will form north of the state Wednesday. As this feature drifts southward near or over the islands Thursday into Saturday, the trade winds could ease further, and chances for heavy showers will likely increase.
Near shore buoys are showing signs of fading energy in the 12 to 16 sec range suggesting the current south swell is slowly beginning to fade today into Wednesday. Forerunners from a larger and longer lived south- southwest swell will arrive Wednesday, and surf is expected rise near, or to, the High Surf Advisory level during the peak of the swell Thursday and Friday. This swell will gradually decline through the weekend.
A small northwest swell of around 3 feet will peak today, then decline Wednesday. Wind- driven waves will gradually decline to around May average today, then drop to below average for the rest of the week.

HFO Watches/Warnings/Advisories

High Wind Warning until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov