Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny. Scattered showers in the afternoon. Highs around 83 near the shore to around 70 above 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers in the evening, then mostly cloudy with isolated showers after midnight. Lows around 67 near the shore to around 58 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Tuesday: Partly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 83 near the shore to around 70 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny with isolated showers. Highs 76 to 83. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 67. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 78 to 83. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 70 to 77 in the valleys to around 62 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 65 in the valleys to around 55 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tuesday: Breezy. Mostly cloudy with scattered showers. Highs 70 to 77 in the valleys to around 61 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 72 to 83. Southeast winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 70. Southeast winds up to 15 mph. Chance of rain 40 percent.

Tuesday: Partly sunny with scattered showers. Highs 72 to 83. East winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 69 to 79. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 71. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 70 to 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy easterly trade winds will gradually ease today. Modest rainfall will favor typical windward slopes, though leeward areas may experience an isolated shower. Breezy and gusty trade winds will return Wednesday along with a wetter tradewind pattern through at least Friday.

Discussion

A weakening high sitting roughly 900 miles northeast of the state is driving breezy easterly trades that will gradually ease today. A mid- to low- level ridge continues to produce stable conditions with an inversion based around 5,000 to 6,000 ft based on the latest soundings. The soundings also shows precipitable water vapor values are on the rise along with an increase in saturation in the mid to upper levels, in line with the presence of stable stratocumulus and upper level cirrus clouds. The increase in moisture in these levels is due to an upper level low several hundred miles south of the state that is also providing breezy southerly winds over the high summits. Overnight windward rainfall remains modest with rather dry conditions leeward.
Guidance still suggests that the weak low- level ridge will inhibit a significant increase in rainfall into Tuesday. However, low clouds and a few spotty showers cannot be ruled out over leeward terrain each afternoon and evening through Tuesday due to lingering instability from the upper level low and possible hybrid land seabreeze pattern.
A return to breezy and gusty trade winds will occur Wednesday into at least Friday as another strong surface high sets up north of the state. The forecast shows upper level temperatures cooling again due to an incoming shortwave trough enhancing instability over the state. This along with lingering moisture in the mid to low levels could provide a wetter pattern tradewind pattern through Friday. In addition, the GFS and ECMWF show a band of moisture from a remnant boundary embedded in the tradewinds further boosting windward rainfall Friday or Saturday but continue to vary on timing.

Aviation

Light to locally moderate trade winds expected through twenty-four hours and beyond. Bands of scattered light showers off the Pacific will favor east and northeast facing slopes and coasts. Brief periods of MVFR in showers are possible, especially over East Maui and Windward Big Island.
AIRMET TANGO remains in effect for moderate low-level mechanical turbulence over and downslope of the mountains from Molokai through Big Island. The general trend is for decreasing winds aloft, so conditions are not expected to extend beyond early evening.

Marine

A large area of high pressure approximately 850 nautical miles northeast of Oahu is driving these recently fresh to locally strong trade winds. This high will slowly drift to the east and weaken the pressure gradient back toward the islands enough to gradually weaken trades to more moderate magnitudes by this evening. Relatively weaker short term winds has the ongoing Small Craft Advisory (SCA) geographically-structured to include all waters except the smaller island leeward waters and Maalaea Bay through the afternoon hours. An incoming moderate size northwest swell, in addition to fresh trade flow, will peak significant coastal sea heights to around SCA thresholds (10 feet) through this afternoon. The next surface high center to build in north of the islands during the middle of the week will again re-tighten the gradient back across the region. This will result in re- strengthening trades back to fresh to locally strong levels by Wednesday morning. Trades may reach gale force speeds within the Alenuihaha Channel and south of Big Island by Wednesday night or early Thursday morning.
A moderate size, long-transitioning-to-medium period west-northwest (300-320 degree) swell will build in this morning and peak this afternoon. This swell will lift surf along better exposed north and west-facing shores to near High Surf Advisory (HSA) levels today. The more westerly component of this swell may bump surf up along the west-facing shores of Big Island today. Island shadowing with the more north (than west) directional component to this swell should keep Kona coast surf under HSA levels. Today's fresh trades will continue to produce short period easterly elevated wind wave swell that has resulted in persistent choppy conditions along most eastern exposures. South-facing shore surf will remain at background levels the next several days. South surf may see a minor bump Tuesday as a very small, medium period south-southwest (200 degree) swell passes around the islands.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for north and west facing shores of Niihau Kauai Oahu Molokai and north facing shores of Maui.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov