Photo Credit: Laila Reiss

West Side

Today: Mostly sunny with isolated showers. Highs 73 to 88. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 62 to 72. East winds up to 15 mph. Chance of rain 40 percent.

Wednesday: Partly sunny with scattered showers. Highs 71 to 87. East winds up to 15 mph. Chance of rain 40 percent.

South Side

Today: Sunny. Highs 75 to 86. North winds up to 15 mph.

Tonight: Mostly clear. Isolated showers after midnight. Lows 64 to 69. North winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 73 to 85. North winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

North Shore

Today: Partly sunny with scattered showers. Highs 75 to 80 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 72 near the shore to 49 to 54 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 75 to 80 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Central Maui

Today: Sunny and breezy. Highs 78 to 85. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon.

Tonight: Partly cloudy with isolated showers. Lows around 67. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny with scattered showers. Highs 78 to 84. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Upcountry

Today: Partly sunny with scattered showers. Highs 50 to 70. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 46 at the visitor center to around 42 at the summit. Southeast winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 50 to 69. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 50 percent.

East Maui

Today: Partly sunny with scattered showers. Highs 75 to 80 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 72 near the shore to 49 to 54 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 75 to 80 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Lanai City

Today: Mostly sunny with isolated showers. Highs 66 to 78. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 58 to 65. Northeast winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny with scattered showers. Highs 67 to 77. Light winds becoming north around 10 mph in the afternoon. Chance of rain 40 percent.

Kaunakakai

Today: Sunny. Highs 64 to 86. East winds 10 to 15 mph.

Tonight: Partly cloudy with isolated showers. Lows 55 to 72. East winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny with scattered showers. Highs 64 to 86. East winds 10 to 15 mph. Chance of rain 50 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.

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Data Courtesy of NOAA.gov