Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 81 near the shore to around 69 above 3000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 68 near the shore to around 57 above 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Wednesday: Breezy. Sunny with isolated showers. Highs around 82 near the shore to around 70 above 3000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 64 to 69. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Wednesday: Windy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 81. Northeast winds 20 to 30 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then occasional showers in the afternoon. Highs 68 to 76 in the valleys to around 63 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 57 to 62 in the valleys to around 51 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Windy. Showers likely in the morning, then scattered showers in the afternoon. Highs 69 to 77 in the valleys to around 64 above 4000 feet. East winds 10 to 35 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 73 to 80. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 60 to 69. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Breezy. Mostly sunny with scattered showers. Highs 74 to 81. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 73 to 80. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 58 to 71. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 81. Northeast winds 10 to 25 mph. Chance of rain 50 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.

Data Courtesy of NOAA.gov