Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with isolated showers. Highs 80 to 86 near the shore to around 70 above 3000 feet. Northeast winds up to 10 mph in the morning becoming light. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 64 to 70 near the shore to around 56 above 3000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 81 to 87 near the shore to around 72 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny with scattered showers. Highs 79 to 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 66. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Sunday: Partly sunny with isolated showers. Highs 80 to 88. Northeast winds around 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Mostly cloudy with scattered showers. Highs 68 to 75 in the valleys to around 61 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 57 to 63 in the valleys to around 53 above 4000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Sunday: Cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 71 to 78 in the valleys to around 64 above 4000 feet. Light winds. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 71 to 81. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 68. Light winds. Chance of rain 40 percent.

Sunday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 73 to 83. Southeast winds up to 10 mph shifting to the northeast around 10 mph in the afternoon. Chance of rain 40 percent.

East Kaua’i

Today: Mostly cloudy with scattered showers. Highs 69 to 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 58 to 70. North winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Sunday: Mostly cloudy with isolated showers. Highs 71 to 82. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Light to moderate trade wind flow, will keep limited shower coverage focused across mainly windward areas through tonight. Humidity will increase Sunday through Monday, as deep tropical moisture lifts through the area. Locally heavy showers may develop over portions of the Big Island Sunday, possibly spreading across interior sections of the smaller islands Monday and Tuesday.

Discussion

Radar shows northeast flow is focusing scattered showers across favored windward areas this morning. The areal coverage of showers has increased some early this morning, as a narrow band of enhanced moisture drifts in from the northeast. The airmass this morning remains mostly stable which should continue to limit rainfall rates through today. Northeast winds have weakened over the state this morning, and will continue to diminish today, as the pressure gradient north of the state continues to weaken.
This weekend, the pressure gradient will further weaken, allowing background winds to relax enough to support some local afternoon sea breeze and night time land breeze circulations. Dry and stable air (modeled moisture depths under 7k ft and low moisture stability index) will support limited chances for showers across the islands later today through early Sunday. The airmass in place early this weekend, will continue cooler temperatures again today, as the airmass remains similar to Friday. Tropical moisture begins to advance northward toward the state Sunday through Sunday night, as a weakly organized feature lifts northward toward the region. Model progs show moisture depths increasing quickly to well above 14kft, with forecast PW values increasing to above 1.75 inches across the eastern end of the state. This pattern will increase the chance for rain, particularly the Big Island and vicinity, Sunday.
Monday through Wednesday, models continue to favor a period of deeper layered moisture and decreasing stability over the state through the period, as the weakly organized feature lifts toward the western end of the islands. Deeper layered moisture and weak instability are forecast across the entire island chain through the first half of next week. Thunderstorm probabilities are supporting some hint, that a thunderstorm or two is also possible in the region through Tuesday, though confidence in thunderstorm chances remains low at this time. The low level pressure gradient will remain weakly organized, with the light southeast flow potentially supporting some afternoon sea breezes through Tuesday, possibly enhancing afternoon leeward showers. Overall, the most likely chance of persistent shower activity island-wide…would be starting Sunday afternoon in the vicinity of the Big Island and Maui, then spreading across the remainder of the smaller central islands early Monday, and then to Kauai Monday afternoon as stability decreases and upper jet dynamics (near the right entrance) combine over the region. Precipitable water values are forecast to increase to above 1.80 inches uniformly across the islands during this time. However, with the main background flow south to southeast, the Big Island may block much of this increased moisture, with less rainfall reaching the smaller islands. Areas along the southeast slopes of the Big Island, the Pahala and Volcano areas, will likely see the best chances for enhanced rainfall amounts.
Thursday into next weekend. Model solutions differ on the exact evolution of the surface feature and tropical moisture lingering over the state, as the feature exits north-northwest of the state. However, current trends support a return toward a trade wind weather pattern developing Thursday into early next weekend.

Aviation

A low pressure system far northeast of the state will continue to drift northward this morning, further from the islands, which will allow the pressure gradient to weaken. Winds will ease considerably through the day today. With relatively dry air in place, expect only isolated showers to affect windward portions of the islands with partly cloudy skies and VFR conditions elsewhere.
There are currently no AIRMETs in effect.

Marine

Combined seas near 17 feet (primarily due to N swell) prevail in exposed areas this morning, thus the Small Craft Advisory (SCA) has been continued for all zones into Sunday, except for Maalaea Bay, where winds and seas have dropped below SCA criteria overnight. A High Surf Warning (HSW) for N facing shores of most islands will remain posted through tonight and now includes portions of the W facing shores of the Big Island (primarily for the area around Kua Bay). A High Surf Advisory (HSA) has been issued for west facing shores of Maui and north facing shores of Lanai as this swell peaks today. A Marine Weather Statement is also posted, alerting boaters about the potential for moderate to strong harbor surges in north facing harbors. A large NNE swell will combine with an early morning high tide this morning and early Sunday morning, bringing the potential for wave runup onto nearshore roadways and properties along exposed N and E shores, i.e., Hilo's Bayfront Highway.
A slow-moving, formerly storm-force, low centered about 700 nm NE of the islands has generated NNE (010-040 degrees) swell roughly 4-6 feet above guidance and will continue to build locally today, as the current N (360 degrees) swell gradually eases. This low will drift slowly N and weaken over the next 24-48 hours as a a ridge builds N of the islands. During this transition, current moderate to fresh NE winds will veer E in the gentle to moderate range into Sunday, then E to SE in the light and variable range into Monday. Confidence in the extended range of the marine forecast is low due to drastic model difference in the potential formation of a tropical low to the W of the islands early next week.
The NNE swell will gradually ease Sunday and Monday, while a small long-period WNW (310 degrees) swell arrives Saturday and Sunday. Another long period WNW (310 degrees) swell is expected late Monday and Tuesday, with peak surf heights nearing HSA levels. Another, slightly larger, WNW (310 degrees) swell arriving Thursday and Friday could produce peak surf heights well into HSA levels. Other than NNE swell wrapping into exposed E facing shores, little surf is expected elsewhere.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 AM HST Sunday for Niihau, Oahu North Shore, Olomana, Maui Windward West, Kohala, Kauai North, Kauai East, Koolau Windward, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
High Surf Advisory until 6 AM HST Sunday for Maui Leeward West, Lanai Windward.
Small Craft Advisory until 6 AM HST Sunday for all Hawaiian waters except Maalaea Bay,

Data Courtesy of NOAA.gov