Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny. Windy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 84. East winds 10 to 25 mph shifting to the northeast 20 to 30 mph in the afternoon. Chance of rain 40 percent.

Tonight: Windy. Partly cloudy with isolated showers. Lows 63 to 69. Northeast winds 25 to 30 mph. Chance of rain 20 percent.

Wednesday: Windy. Sunny with isolated showers. Highs 78 to 85. Northeast winds 25 to 35 mph with gusts to 60 mph. Chance of rain 20 percent.

South Side

Today: Sunny and breezy. Highs around 84. Northeast winds 10 to 20 mph.

Tonight: Mostly clear. Breezy. Lows around 64. Northeast winds 10 to 25 mph.

Wednesday: Sunny and windy. Highs around 85. Northeast winds 15 to 30 mph with gusts to 50 mph.

North Shore

Today: Mostly cloudy. Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 76 to 81 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 61 to 67 near the shore to around 49 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Windy. Scattered showers. Highs 77 to 82 near the shore to around 62 near 5000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Central Maui

Today: Breezy. Mostly sunny with isolated showers. Highs around 82. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows 62 to 68. Northeast winds 20 to 25 mph. Chance of rain 20 percent.

Wednesday: Sunny and windy. Isolated showers in the morning. Highs around 83. Northeast winds 20 to 30 mph. Chance of rain 20 percent.

Upcountry

Today: Breezy. Mostly sunny with scattered showers. Highs around 54 at the visitor center to around 50 at the summit. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Windy. Scattered showers in the evening. Lows around 43 at the visitor center to around 38 at the summit. East winds 10 to 30 mph. Chance of rain 50 percent.

Wednesday: Sunny and windy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 54 at the visitor center to around 50 at the summit. East winds 10 to 35 mph. Gusts up to 55 mph in the afternoon. Chance of rain 50 percent.

East Maui

Today: Mostly cloudy. Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 76 to 81 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 61 to 67 near the shore to around 49 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Windy. Scattered showers. Highs 77 to 82 near the shore to around 62 near 5000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Lanai City

Today: Sunny and breezy. Isolated showers in the afternoon. Highs 71 to 78. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Lows around 63. Northeast winds 15 to 25 mph.

Wednesday: Sunny and windy. Isolated showers in the afternoon. Highs 72 to 79. Northeast winds 15 to 35 mph increasing to 25 to 35 mph in the afternoon. Gusts up to 55 mph. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 71 to 82. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows 56 to 68. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Wednesday: Sunny and windy. Isolated showers in the morning. Highs 72 to 83. Northeast winds 20 to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy trade winds will become strong and gusty Wednesday, then continue into the weekend. Clouds and showers will focus over windward areas, with occasional brief showers spreading to leeward locations.

Discussion

Latest satellite images show an area of increased low-level moisture moving toward the islands from the E, with embedded showery clouds extending as high as 20 thousand feet. Radar is beginning to detect some of these showers, mainly over windward portions of the Big Island and Maui, with a few small pockets of moderate to heavy showers. Morning sounding from Lihue shows a weak subsidence inversion near 7000', while the Hilo sounding shows drying above that level, with a lack of an inversion.
High pressure centered far NE of the islands will support moderate to locally breezy trade winds through tonight. A new high building N of the area on Wednesday will move steadily E while strengthening to near 1040 mb by Friday. The resulting pressure gradient will support windy conditions from Wednesday through Friday, with wind speeds likely becoming strong enough to warrant a Wind Advisory for many areas. The high will gradually weaken in the NE Pacific over the weekend, only to strengthen again early next week. Expect breezy to strong trade winds to prevail into next week.
Main short-term forecast challenge hinges on the prognosis of the approaching cloud and shower band, and how much of it will move ashore on Kauai and Oahu. Guidance indicates the bulk of the moisture will move over Maui and the Big Island through the day, fueling primarily windward showers. An increase in windward showers will also likely occur over Kauai and Oahu as well later this morning. Rainfall amounts will be limited due to the fast forward speed of the showers, and the relative stability of the atmosphere.
Guidance continues to advertise drier air moving over the islands tonight and Wednesday. This looks to be true, judging by the stable low cloud field between 140W and 150W, and fewer showers can be expected. By Thursday, a developing weak trough aloft S of the islands will bring mid-level cooling, and the strong trades will provide orographic lift. This will likely result in periods of brief windward showers, with the strong trades blowing some light rain leeward on the smaller islands. Little significant change is expected through the weekend, with potential for wetter weather early next week as the trough aloft moves N over the islands.

Aviation

Locally breezy trade winds will persist today, then become strong and gusty tomorrow. The majority of showers and low clouds will focus over windward areas through the TAF period. The increasing winds may briefly push a few light showers to leeward areas. Mainly VFR conditions are expected across TAF locations, however MVFR conditions are expected across some windward locations in heavier showers. MVFR conditions could become extensive enough over windward Big Island and Maui to warrant AIRMET Sierra for mountain obscuration.
AIRMET Tango will remain in place for low level turbulence over and downwind of island terrain during the next several days.

Marine

A large surface high centered far northeast of the islands is producing fresh to locally strong trade winds across the Hawaiian waters. As a new high passes to the north during the second half of this week, these trades will become even stronger across all waters. The Small Craft Advisory (SCA) remains in effect through Thursday afternoon for strong trades across the typical windy waters around Maui County and the Big Island, as well as the windward Oahu and Maui waters. A Gale Watch is also in effect for the aforementioned typical windy waters beginning Wednesday morning as the trades increase. The SCA will likely need to be expanded westward to include all waters beginning Wednesday.
The current northwest (310-320 degree) swell has filled in across the local waters and will gradually build over the next day or so. Surf along north and west-facing shores will rise accordingly and peak Wednesday, before fading Thursday. A north (340-350 degrees) swell is expected to arrive Thursday, with surf building to around High Surf Advisory levels for north and west facing shores as it peaks into the evening. This swell will decline Friday into the weekend. Rough sea conditions can be anticipated along eastern shores in response to strong to near gale force trades over and upstream of the area. Surf heights may even reach advisory levels Friday and Saturday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Thursday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Watch from Wednesday morning through Thursday afternoon for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov