Photo Credit: Jason Weingardt

West Kaua’i

Today: Partly sunny early in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs around 82 near the shore to around 70 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 near the shore to around 57 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 81 near the shore to around 69 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs around 81. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 64 to 69. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 80. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with scattered showers. Highs 69 to 77 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Showers likely in the evening, then occasional showers after midnight. Lows 57 to 62 in the valleys to around 51 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Tuesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 68 to 76 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 74 to 81. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 60 to 69. East winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 73 to 80. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 74 to 81. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 58 to 70. East winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 80. East winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate to breezy trade winds will become strong and gusty by Wednesday, with windy conditions continuing into the weekend. Showers will continue across the islands through Tuesday, mainly focused across windward areas and the Big Island. Drier and more stable conditions are expected by mid-week which will limit showers across the islands into Saturday.

Discussion

Current radar shows showers scattered across the islands this morning, focused mainly along windward slopes as locally breezy trade winds continue. Radar shows the greatest concentration of showers across portions of the Big Island and Maui. Additionally, lightning data shows several strikes occurring in the vicinity of Big Island, around 160 miles south of South Cape, in a board area of enhanced instability (Showalter Index (SW) between 0 to -2c). Radar estimates suggest locally enhanced rainfall embedded within some of the showers this morning drifting over Big Island and Maui.
Today through Tuesday…high pressure centered well northeast of the state will maintain moderate to locally breezy trades through the period. The upper low, which had been centered across the state during the weekend, will weaken and become centered southeast of Big Island while an upper ridge builds in across the western end of the state. Showers across the eastern end of the state, in the vicinity of Big Island, will be capable of generating locally heavy rainfall into this afternoon as satellite based PW values (around 1.65″) continue to stream in from the east. Overall expect showers to continue across much of windward Big Island today with locally heavy rainfall possible, as modeled moisture depths remain elevated about 15k and moisture stability index supports some enhanced rainfall. Will also mention a few thunderstorms this morning for portions of the Big Island, as an area of weak instability (SW around 0 to -1c) stretches from Hilo to South Cape and extends into surrounding marine waters. However stability increasing this afternoon will hinder thunderstorm activity, which matches well with modeled thunderstorm probabilities lessening drastically by this afternoon. Across the rest of the islands, will maintain showers across mainly windward areas as moisture depths linger between 9k to 13k ft and PW values linger around 1.30″. Breezy trades could briefly push showers to leeward areas also. Additionally, moisture extending to the summits of Mauna Kea and Mauna Loa, will generate a period of freezing rain or light snow, therefore the Winter Weather Advisory will continue through noon today. Tuesday, the trend toward drier and more stable conditions will begin to limit rainfall intensity and slowly reduce the areal coverage of showers across the islands.
Wednesday through next weekend…model trends continue to support dry and stable conditions into Saturday, with forecast PW values under 1.00″ while modeled moisture depths fall to around 8k ft or less. This pattern will greatly reduce the intensity and areal coverage of showers across the islands. High pressure building north of the area on Wednesday will lead to strengthening trade winds, with windy conditions expected into the weekend. Wind speeds may become strong enough to warrant a Wind Advisory. Trade winds will maintain showers across mainly windward locations, with the most persistent shower coverage at night through early morning. However, the gusty trade winds will occasionally push showers to leeward areas. The areal coverage of showers could increase across windward areas during the second half of the weekend, as an area of moisture (south of the state) potentially lifts up across the islands as an upper low tries to reorganize and lift northward. This pattern could once again enhance rainfall intensities for portions of the state Sunday through Monday.

Aviation

Breezy trades will prevail, with clouds and showers favoring windward areas. Increased cloud and shower coverage across windward and southeast sections of the Big Island will continue today as an area of moisture is pushed ashore by the trades. An upper trough to our east will enhance these showers and introduce the possibility of thunderstorms, primarily for the eastern end of the Big Island. AIRMET Sierra, for mountain obscurations, remains in effect for windward Big Island areas. However, VFR conditions will prevail across the rest of the state. AIRMET Tango, for moderate low-level turbulence, will continue over and downwind of island mountains.

Marine

Fresh to strong easterly trade winds will continue through Tuesday, then become strong for all Hawaiian waters Wednesday into next weekend as high pressure passes to the north. As a result, the Small Craft Advisory currently in place will hold through Tuesday over the windier channels and waters from Oahu to the Big Island, then likely become expanded to all waters beginning Wednesday. Seas will respond and become rough over exposed waters, quickly building to the advisory level of 10 ft Wednesday due to a combination of the strong winds and a northwest well moving through.
Surf along north and west facing shores will gradually climb through the day today as a fresh long-period northwest swell builds down the island chain. Swell heights at the offshore NDBC buoys 51101 and 51001 have been building overnight within the 19-21+ second bands and have recently picked up slightly at the nearshore PacIOOS buoy near Hanalei. Guidance shows this source peaking tonight through midweek before fading into Thursday. A new north-northwest swell arriving Thursday from a developing gale west of the Date Line today will drive surf up along exposed shores toward advisory levels as it peaks late Thursday through Thursday night. As this source begins to ease Friday into the weekend, no other significant swell sources are expected.
Surf along east facing shores will quickly ramp up Wednesday as the strong trades expand over the state and upstream over the eastern Pacific. Heights may near advisory levels by the weekend.

HFO Watches/Warnings/Advisories

Winter Weather Advisory until noon HST today for Big Island Summits.
Small Craft Advisory until 6 PM HST Tuesday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov