Photo Credit: Braden Jarvis

West Kaua’i

Today: Sunny and breezy. Highs around 89 near the shore to around 77 above 3000 feet. East winds up to 20 mph.

Tonight: Partly cloudy. Breezy. Isolated showers late in the evening. Scattered showers after midnight. Lows around 72 near the shore to around 61 above 3000 feet. East winds up to 20 mph becoming 10 to 15 mph after midnight. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 86 to 91 near the shore to around 77 above 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs 81 to 89. East winds 15 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 73. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 82 to 89. East winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 86 in the valleys to around 66 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 70 in the valleys to around 59 above 4000 feet. East winds up to 20 mph. Chance of rain 60 percent.

Thursday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 85 in the valleys to around 66 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs 77 to 90. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 73. East winds up to 15 mph shifting to the southeast after midnight. Chance of rain 50 percent.

Thursday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 77. Northeast winds up to 15 mph. Chance of rain 60 percent.

Thursday: Partly sunny with scattered showers. Highs 74 to 87. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Gusty trade winds, low relative humidity, and dry fuels will result in fire weather concerns from late this morning through the afternoon across leeward sections of all islands today. Otherwise, brief clouds and showers will favor mainly windward areas. Showers are expected to increase tonight through Friday night as a mid-level trough moves through. Winds will also taper off Thursday night into Friday. A drier trend is expected this weekend with strengthening trade winds.

Discussion

Broad ridging north and northeast of the islands will continue to produce locally strong trade winds across the islands today. Although winds will be similar or slightly weaker than yesterday for most locations, slightly drier air is anticipated to settle over the islands, allowing relative humidity values to dip into Red Flag Warning criteria. See the Fire Weather section below for details. Also of note, the strong advisory-level winds that were observed across the Big Island summits yesterday afternoon and evening have sharply declined overnight. Therefore, the Wind Advisory for Big Island summits has been cancelled with this morning's forecast updates.
Early morning 12z soundings from Lihue and Hilo showed strong trade wind inversions between 7,000 and 9,000 feet. Trades will carry brief clouds and showers into the islands today, focusing mainly over windward and mauka areas. However, guidance indicates that conditions are expected to be generally stable over the state today, limiting rainfall amounts in most locations.
A mid-level trough will move over windward and southeast Big Island tonight, then spread westward during the second half of the week. This feature will bring an increase in clouds and showers through Friday night. A weak upper level low moving into position northeast of the state during this time may also enhance the incoming showers.
An advancing cold front well north of Hawaii will displace the driving high pressure further northeast of the islands, slightly weakening wind speeds by Thursday night. Meanwhile, a nearly stationary low pressure system will set up northwest of Hawaii. The pressure gradient between these two features will continue to maintain moderate and slightly veered east southeasterly winds into Friday. Island terrain blockage under this wind regime will further weaken the winds across leeward areas, resulting in localized sea breezes and interior clouds Friday afternoon before the trade winds re-strengthen this weekend.
The forecast will trend drier with a continuation of the moderate east southeast flow from Saturday into the middle of next week.

Aviation

Breezy easterly trade winds will prevail during the next 24 hours, with limited low clouds and showers focusing mainly over windward and mountain areas. Predominantly VFR conditions are expected.
AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of the island terrain. This AIRMET will likely be needed through this evening.

Marine

The high pressure ridge north of the island will producing fresh to strong trade winds today with the strongest winds reaching near gale conditions in the windiest eastern channels. The Small Craft Advisory (SCA) remains in effect for the central and eastern waters through tonight. This SCA will then decrease in coverage on Thursday. Trade wind speeds will fall below SCA conditions by Thursday night as the ridge weakens north of the island chain.
The current north (350) medium period swell will continue to slowly decrease just below High Surf Advisory (HSA) thresholds this morning. Therefore, the HSA for north facing shores was cancelled. Surf heights will remain elevated at just below advisory surf height thresholds through the morning hours. Surf along west facing shores remains slightly elevated with wrap around north swell energy lingering for into Thursday.
Surf heights along east shores will remain elevated tonight in response to short period trade wind swell over and upstream of the islands. East shore surf heights will then decline on Thursday as trade wind speeds weaken. South shore surf will remain small this week mainly due to south and southeast background swells into next week. The next small long period south swell pulse will arrive in Hawaii from Friday into Saturday.

Fire weather

A combination of gusty winds, relatively stable and dry conditions, and dry fuels (with Keetch-Byram Drought Index (KBDI) values well over 600) will result in critical fire weather conditions today. A Red Flag Warning has been issued for leeward sections of all the islands from late morning through the afternoon, when relative humidity will be at its lowest and winds will be maximized. As a mid-level trough and upper low nears the eastern end of the state tonight and winds gradually begin to weaken, expect fire weather concerns to diminish for the rest of the week.

HFO Watches/Warnings/Advisories

Red Flag Warning from 10 AM this morning to 6 PM HST this evening for HIZ301, HIZ304, HIZ305, HIZ307, HIZ308, HIZ309, HIZ310, HIZ311, HIZ315, HIZ316, HIZ320, HIZ321, HIZ322, HIZ323, HIZ324, HIZ325, HIZ328, HIZ329, HIZ330, HIZ333, HIZ334, HIZ337, HIZ338, HIZ341, HIZ342.
Small Craft Advisory until 6 AM HST Thursday for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov