Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Locally heavy rainfall possible in the morning. Highs around 81 near the shore to around 69 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 69 near the shore to around 56 above 3000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 80 near the shore to around 68 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 76 to 82. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Locally heavy rainfall possible. Lows around 65. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs 77 to 82. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Breezy. Cloudy with frequent showers in the morning, then partly sunny with scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 68 to 75 in the valleys to around 60 above 4000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with frequent showers. Locally heavy rainfall possible. Lows 57 to 64 in the valleys to around 54 above 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain 90 percent.

Tuesday: Cloudy and breezy. Frequent showers in the morning, then frequent showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 67 to 74 in the valleys to around 61 above 4000 feet. Northeast winds 15 to 20 mph. Chance of rain 90 percent.

North Kaua’i

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 71 to 81. East winds up to 20 mph becoming 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with frequent showers. Locally heavy rainfall possible. Lows 59 to 68. East winds 10 to 20 mph. Chance of rain 90 percent.

Tuesday: Cloudy and breezy. Frequent showers in the morning, then frequent showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 70 to 79. Northeast winds 15 to 20 mph. Chance of rain 90 percent.

East Kaua’i

Today: Breezy. Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 69 to 79. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with frequent showers. Locally heavy rainfall possible. Lows 58 to 70. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Tuesday: Cloudy and breezy. Frequent showers in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 68 to 79. Northeast winds 15 to 20 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

A strong high pressure system far northeast of the Hawaiian Islands will slowly drift eastward and produce moderate breezy trades into Tuesday. Weaker winds will develop over the eastern islands Tuesday afternoon as a surface trough moves eastward into Maui and Hawaii Counties. An upper level low will linger over the region this week, producing unstable wet weather statewide, with locally heavy rain and a few thunderstorms lasting into next weekend.

Discussion

Radar shows showers pushing across the islands this morning with the most persistent showers anchored across windward zones and in the vicinity of Big Island and Maui. Radar estimates show locally heavy rainfall rates embedded within showers, nearing 1 to 2 inches per hour. Lightning data shows a few strikes across the eastern end of the state in the Big Island marine waters, extending northeast of Hilo to southwest of Kona.
Today through Wednesday…the breezy trades that have been in place across the islands through the weekend will continue today. The trade winds will then begin to weaken from east to west this week, as a weak surface trough pushes into the eastern portions of the state Tuesday before drifting further westward on Wednesday. The lingering breezy trades today will help push a few showers to leeward areas again today. A 500 mb low northeast of the islands this morning, will slowly drift back across the state through midweek, before moving to a position southwest of the islands Wednesday night. This pattern will likely shift the band of heaviest showers from the Big Island and Maui briefly Tuesday into Wednesday, with more persistent widespread showers focused across the western end of the state. The airmass drifting across the region this week will remain moist, with moisture depths well over 12k ft, to sufficiently maintain showers with locally heavy rainfall. Thunderstorm probabilities and stability indices (SW around 0C) suggest the best chances for thunderstorms early this week, will be over the eastern end of the state and across windward marine waters through Wednesday. Thunderstorm chances diminish greatly across the Big Island and Maui County Tuesday through Wednesday, as drier and more stable air lifts up across the eastern half of the state, as the upper low drifts over the western islands. Additionally, deep moisture reaching summit levels, will continue wintry conditions today, maintaining the need for a Winter Weather Advisory for snowfall across the Big Island summits (above 11,000 feet).
Thursday into the weekend…model solutions continue to trend toward another extended period of potentially significant rainfall spreading across the state Thursday into the weekend. The upper low forecast to slide across the western end of the state Wednesday, will drift into position over 400 miles southwest of the islands Thursday. Current model solutions depict this upper low rotating slowly eastward through the weekend. Forcing associated with the 500mb low, will increase across much of the state Thursday with sufficient forcing lingering through Saturday. Deepening on the act progression and evolution of this upper low, this pattern could lift deep layered tropical moisture northward across much of the state Thursday through Saturday, with forecast PWs increasing from a statewide average of 1.40″ on Thursday, to over 1.80″ Friday and Saturday. Thunderstorm probabilities and SW index also support the chance of some thunderstorms during this time. Overall will maintain current forecast trend of showers spreading across the islands through the period, with heavy rainfall possible through Saturday, before showers and heavy rainfall potentially diminishing Sunday.

Aviation

Expect moderate to breezy trade winds blowing across the Hawaii region today. A weak upper level low over the islands will continue to produce periods of showers falling mainly over windward and mountain slopes of each island. A surface trough will form under this upper low just east of the Big Island today. This trough will drift slowly westward and weaken trade wind speeds over Maui and Hawaii Counties later tonight through Tuesday.
Mostly VFR conditions are expected with brief MVFR conditions in showers mainly over mountain areas and along north and east slopes of each island, favoring the overnight to early morning hours. Locally heavy showers and thunderstorms are expected today from Molokai to the Big Island today, spreading statewide by Tuesday.
AIRMET Sierra remains in effect for mountain obscuration across north and east sections of Kauai, Oahu, Molokai, Maui and the Big Island. Coverage of these conditions will decrease later this morning.
AIRMET Tango remains in effect for low level moderate turbulence over and immediately south through west of island mountains. Conditions will improve later this morning over the eastern islands.

Marine

Strong to near gale force trades will continue today and tonight, as high pressure remains anchored northeast of the islands. As a result, a Small Craft Advisory (SCA) is now in effect for all waters through 6 AM Tuesday. A trough of low pressure will develop southeast of the state tonight, then slowly track westward across the islands Tuesday through Thursday. The trades will shift northeasterly and remain strong ahead of the trough, with moderate to strong southeasterlies developing behind the trough. Strong to near gale force trade winds could return to portions of the marine area on Friday.
The High Surf Advisory (HSA) has been extended through 6 AM Tuesday for east facing shores due to large and rough trade wind swell. East shore surf will remain above seasonal levels through late in the week due to strong trades over and upstream of the islands. The HSA may need to be extended for Kauai and Oahu, potentially through late in the week, where the winds over and upstream will remain the strongest. A pair of northwest swells will give north shore surf a boost this week. The first swell will peak just below the advisory threshold today, then decline tonight and Tuesday. A second northwest swell will build on Wednesday, peak below advisory levels Thursday, and decline Friday. South facing shores will experience minimal surf this week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for Olomana, Kahoolawe, Maui Windward West, Kauai East, Kauai South, East Honolulu, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, South Haleakala, Big Island Southeast, Big Island East, Big Island North.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 AM HST Tuesday for all Hawaiian waters,

Data Courtesy of NOAA.gov