Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 81. Northeast winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 60 to 66. East winds up to 15 mph. Chance of rain 20 percent.

Saturday: Mostly sunny. Isolated showers in the morning. Highs around 81. Southeast winds up to 10 mph. Chance of rain 20 percent.

South Side

Today: Mostly sunny. Highs around 83. Light winds.

Tonight: Partly cloudy. Lows 60 to 66. West winds up to 10 mph in the evening becoming light.

Saturday: Mostly sunny. Highs around 83. Light winds becoming west around 10 mph in the afternoon.

North Shore

Today: Breezy. Partly sunny with isolated showers. Highs 77 to 82 near the shore to around 64 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 58 to 66 near the shore to around 48 near 5000 feet. Southeast winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain 70 percent.

Saturday: Breezy. Partly sunny with showers likely in the morning, then mostly sunny with scattered showers in the afternoon. Highs 77 to 82 near the shore to around 61 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Central Maui

Today: Mostly sunny. Highs around 83. East winds up to 15 mph.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Lows 59 to 64. East winds up to 15 mph.

Saturday: Mostly sunny. Highs around 83. East winds up to 15 mph.

Upcountry

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 59 at the visitor center to around 55 at the summit. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 44 at the visitor center to around 40 at the summit. Southeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 55 at the visitor center to around 51 at the summit. East winds up to 10 mph. Chance of rain 50 percent.

East Maui

Today: Breezy. Partly sunny with isolated showers. Highs 77 to 82 near the shore to around 64 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 58 to 66 near the shore to around 48 near 5000 feet. Southeast winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain 70 percent.

Saturday: Breezy. Partly sunny with showers likely in the morning, then mostly sunny with scattered showers in the afternoon. Highs 77 to 82 near the shore to around 61 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Lanai City

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 69 to 76. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows around 62. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 69 to 76. Light winds. Chance of rain 40 percent.

Kaunakakai

Today: Mostly sunny. Isolated showers in the afternoon. Highs 72 to 82. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 54 to 66. East winds up to 15 mph. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs 72 to 82. East winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy east to east-southeasterly trade winds will prevail over the eastern islands, with light to moderate east-southeast trades along with leeward land and sea breezes expected over the western end of the state. Showers will focus mainly along windward and southeast slopes into Sunday. A passing upper-level trough will bring some instability today through Saturday, leading to an uptick in rainfall intensity and triggering a few showers over sheltered leeward areas in the afternoon. Winds will shift out of the south, and showers may increase late Sunday, mainly on Kauai and Oahu. A front is expected to move down portions of the island chain Monday through Tuesday, bringing the potential for heavy rainfall and thunderstorms. Another cold front could bring some more unsettled weather next Thursday.

Discussion

Currently at the surface, a weak 1011 mb low is located around 625 miles west-northwest of Kauai, with a surface trough extending both northeast and south of the low. Meanwhile, a 1033 mb high is centered around 1400 miles northeast of Honolulu. The positioning of these features is bringing east-southeasterly trade winds to the island chain early this morning, with moderate to locally breezy conditions in unsheltered sections of the eastern islands, while lighter winds prevail over the western end of the state where land breezes have developed in leeward locales. Infrared satellite imagery shows variably cloudy conditions with cloud coverage the highest over Kauai and in windward areas of the other islands. Radar imagery shows some light showers moving into windward and southeast facing slopes and coasts, with mainly dry conditions in leeward locales. Not too far west of the state scattered to numerous thunderstorms are present closer to a cold pool aloft. Main forecast concern continues to be on an incoming cold front and potential weather impacts Sunday night through early next week.
Little change in the overall wind regime is expected during the next couple days as high pressure remains anchored northeast of the state. Moderate to locally breezy east-southeast trades will persist in unsheltered sections of the eastern islands, while lighter winds prevail over the western end of the state where widespread leeward land and sea breezes will continue. Winds will gradually ease over the eastern end of the state Saturday night and Sunday, with the low level flow becoming more southerly at light to moderate speeds as a cold front begins to approach from the west. Southerly winds will continue to ramp up in advance of the front Sunday night, with breezy south to southwest winds expected Monday through Tuesday as the front moves into the islands and stalls out. The winds appear to diminish to moderate levels out of the southwest on Wednesday, with the potential for another strong surge of southwest winds, potentially very strong, in advance of yet another cold front next Thursday.
As for the remaining weather details, the east-southeasterly boundary layer flow will favor showers affecting windward and southeast facing slopes and coasts during the next several days. A few showers will be possible over leeward and interior sections of the islands each afternoon and early evening as well due to sea breeze development. A upper low/trough will approach from the west today, then move from eastward across the state tonight through Saturday night. Although the airmass will destabilize as this feature approaches and moves through, moisture return will be limited. Nonetheless, the added instability will likely increase shower coverage and intensity a bit, particularly tonight and Saturday, possibly into Saturday night, as the disturbance aloft moves through. A few thunderstorms may affect Niihau and the nearshore waters west of Kauai today and tonight, but are not expected to reach the island of Kauai.
Attention then turns to a more significant weather maker, as a cold front approaches from the west Sunday night and Monday, then slowly shifts eastward through the smaller islands Monday night and Tuesday. This will bring a rather unsettled period to the islands with widespread rainfall, heavy at times, along with embedded thunderstorms. A Flood Watch will likely be required for much if not all of the state at some point this weekend. The front is forecast to stall out and gradually dissipate in the vicinity of Maui County Tuesday night and Wednesday, keeping some lingering shower activity over the islands although the rainfall intensity should decrease. Another strong cold front appears to bring another round of showers and possibly thunderstorms to the islands next Thursday, but there is more uncertainty with this front as there remains some important model details that have yet to be resolved.

Aviation

Strong high pressure in the Northeast Pacific will keep moderate to locally breezy southeasterly winds in place through the remainder of the week. Sea breezes will predominate in the afternoons across sheltered leeward portions of Oahu, Maui, and the Big Island.
The air mass over the state will remain dry. Shower activity will be limited in both coverage and intensity, and favor southeast facing slopes and coasts. Expect mainly VFR conditions, with brief periods of MVFR under passing showers.
Brisk east winds at summit level will necessitate the continuance of AIRMET Tango for low level turbulence over and downstream of Maui and the Big Island.

Marine

Moderate to strong east to southeast winds will prevail over the eastern waters, while light to moderate east-southeast winds hold over the western waters through today. Winds will weaken slightly Saturday before veering southerly Sunday. Winds will then shift out of the south southwest and strengthen briefly to moderate to locally strong speeds during the first part of next week as a front moves down portions of the state. The combination of a large northwest swell and strong trade winds upstream will build seas to 10 feet or greater over most of the coastal waters today. The Small Craft Advisory (SCA) has been extended for most waters through 6 AM Saturday. However, some zones may drop out before then if seas ease faster than expected due to the passing northwest swell.
A high end High Surf Advisory has been extended through 6 AM Saturday for most north and west facing shores of the smaller islands. The current large, long- period northwest swell seems to have arrived later and a couple of feet bigger than expected, thus the forecast has been adjusted to hold advisory level surf through tonight. A new moderate, long-period northwest swell will build Monday, peak Monday night and Tuesday below advisory level, then gradually decline through the middle of next week.
Surf along east facing shores will remain rough and choppy through Saturday due to locally strong east to southeasterly winds and a wide fetch of strong trade winds upstream. East facing shore surf will gradually decline Sunday into early next week as the upstream trades diminish and local winds veer southerly. Surf along south facing shores will remain small through the weekend, with only background southerly swells. South shore surf could get rough and choppy Monday through the middle of next week as the southerly winds pick up.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov