Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 80 near the shore to around 69 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows 64 to 69 near the shore to around 56 above 3000 feet. Northeast winds 10 to 15 mph.

Monday: Mostly sunny with isolated showers. Highs around 81 near the shore to around 69 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny in the afternoon. Highs 77 to 83. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 65. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs 78 to 85. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs 69 to 76 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 59 to 64 in the valleys to around 54 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 76 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

North Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 71 to 81. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 60 to 69. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 72 to 82. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

East Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 68 to 80. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 60 to 71. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 69 to 82. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Detailed Forecast

Synopsis

Trade winds are expected to increase today due to high pressure building to the northwest of the islands. Showers will become focused over the typical windward areas. Heading into the middle and end of the week, winds are expected to weaken and turn to the southeast. An upper trough could bring enhanced rainfall during the second half of the week.

Discussion

The overall forecast remains the same, but most of the grids have been updated to reflect the latest nuiances of the models.
In the near term, we have high pressure building to the northwest of the islands. Trade winds are expected to continue to build today to locally breezy levels, and persist into Tuesday. A dissipating cold front to the east of the islands, coupled with a weakening upper level trough to the east, are leaving low level moisture that will be carried in on the trade winds. This is expected to result in some typical trade wind showers over the windward and mauka areas. A slightly drier airmass moving over the islands Monday will likely result in fewer showers.
As we head into the middle of the week, the high lifts to the north, which will weaken the trade winds. By Wednesday night, a low pressure system to the northwest will help to shift the winds to a more southeasterly direction. At the same time, the global models show an upper level trough digging down to the west of the islands. The GFS wants to develop a closed upper level low, while the ECMWF keeps it as a trough. Both models indicate thunderstorm potential moving in from the west over the islands Wednesday night and into Thursday. The National Blend of Models isn't as keen on the potential for thunderstorms, but that could be the lack of high resolution models out that far in the forecast.
Have not introduced thunderstorms into the forecast, but that will bear monitoring over the next several days. The presence of an upper level low or trough will very likely mean a wetter end to the week.

Aviation

Light to locally moderate north-northeast trade winds will continue. Bands of showers, the remains of an old frontal boundary, can be seen on satellite moving in from the north- northwest. As of 2am Sunday, radar indicated the strongest showers to be passing over Oahu and Kauai and headed towards Maui and the northern coast of the Big Island. AIRMET Sierra for mountain obscuration is now in effect for Oahu and Molokai. Sierra will likely need to be expanded to include Maui and possibly Windward Big Island later this morning.
Regarding Leeward Big Island, light sea breezes will return later today and drive shower development along south and west facing slopes. A strong inversion aloft around 07 kft, however, will act as a cap–limiting both shower coverage and intensity. Both the sea breezes and the inland showers will taper off quickly after sunset.

Marine

A weak front just east of the island chain will dissipate as it moves northeast today. Northeasterly trade winds will strengthen to moderate to locally strong levels later this afternoon and evening as a high pressure system northwest of the state builds. A Small Craft Advisory has been issued for typically windy areas around Maui County and the Big Island starting at noon today through 6 AM Tuesday. The high pressure will weaken late Monday through the middle of next week, allowing the trades to gradually ease into the light to moderate range.
The current moderate sized north-northwest swell has peaked and will hold through today, with a slow decline and a shift to a more northerly direction tonight through the middle of next week. A High Surf Advisory (HSA) remains in effect for north facing shores of Niihau, Kauai, Oahu, Molokai, and Maui through 6 PM Sunday. The HSA may need to be extended later this afternoon if heights remain elevated above guidance. A new moderate sized north- northeast swell is forecast to build Wednesday night, giving a nice boost to north and east shore surf Thursday with a steady decline to follow Thursday night into next weekend.
A series of south and south-southeast swells will keep south shore surf relatively steady through late next week, at or slightly below the summertime average.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Niihau, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory from noon today to 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov