Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 87 near the shore to around 75 above 3000 feet. Northwest winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 66 to 71 near the shore to around 57 above 3000 feet. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the morning, then showers likely and slight chance of thunderstorms in the late morning and afternoon. Highs around 87 near the shore to around 75 above 3000 feet. Light winds. Chance of rain 70 percent.

South Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84. Light winds becoming southwest around 10 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 64 to 70. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the morning, then showers likely and slight chance of thunderstorms in the late morning and afternoon. Highs around 84. West winds up to 10 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 74 to 81 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 57 to 62 in the valleys to around 52 above 4000 feet. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the morning, then showers likely and slight chance of thunderstorms in the late morning and afternoon. Highs 74 to 81 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 86. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 60 to 70. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the morning, then showers likely and slight chance of thunderstorms in the late morning and afternoon. Highs 77 to 86. West winds up to 10 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 85. Southeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 58 to 72. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the morning, then showers likely and slight chance of thunderstorms in the late morning and afternoon. Highs 77 to 85. West winds up to 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Humid conditions and light winds will continue through much of the week. Showers will begin to increase in coverage across the islands today as some deeper tropical moisture begins to lift northward into the state. More widespread rainfall and perhaps a few thunderstorms will affect the islands tonight through Thursday as a front develops near the western end of the state and slowly tracks east. A cold front may then move over the islands Friday and Saturday, bringing a return of moderate trades and more typical trade wind weather to the island chain.

Discussion

Currently at the surface, a 996 mb low is located around 950 miles north of Honolulu, while a dissipating front is positioned just north of Kauai. The proximity of the front has placed the islands in a light wind regime, with land breezes present in many areas. Infrared satellite imagery shows a mix of low and high clouds, resulting in partly to mostly cloudy conditions across the state. Radar imagery shows scattered showers moving into south facing shores of the islands, with the coverage the greatest over Maui County at the moment. Main forecast concerns revolve around the potential for some more widespread rainfall and thunderstorms tonight through Thursday.
The front just north of Kauai, will dissipate today, with a new front then developing near or over the western islands tonight and Tuesday. The front will remain nearly stationary through Wednesday, before slowly edging eastward and weakening Wednesday night and Thursday. A new cold front is forecast to move southward into the state Friday and Saturday. Overall this pattern is expected to produce an extended period of light winds, with land and sea breezes common in most areas through Thursday. Trade winds could begin to fill in Thursday night, then strengthen to moderate levels Friday through the weekend.
As for the remaining weather details, some deeper moisture is already beginning to move northward into the state, and should bring scattered showers to Oahu and Maui County this morning. Sea breezes should lead to more shower development over the island interiors this afternoon into this evening, with a thunderstorm remaining possible over the Big Island. Tonight, a potent shortwave trough well northwest of the state will dig southeastward toward the deep closed low north of the islands. This will draw additional deep tropical moisture northward into the state. The closed low will open up and lift northeastward on Tuesday, but will quickly be replaced by a potent shortwave trough closing off into another slow moving closed low north of the islands on Wednesday, then shifting eastward Thursday and Friday. This set up is expected to bring a steady influx of deep tropical moisture into the islands with precipitable water values in excess of 2 inches for multiple days. Model guidance remains in good agreement showing that the western islands will have the highest potential for some more significant rainfall totals. Additionally, with large scale forcing for ascent and deep tropical moisture in place, a few rumbles of thunder will be possible over much of the state tonight through Thursday. The deeper moisture should begin to exit the region to the northeast on Thursday, with a new front potentially bringing a more typical trade wind weather pattern back to the islands Friday through next weekend.

Aviation

A low pressure system far north of the state will continue to keep a weak wind pattern in place over all islands. Tropical moisture drifting up from the south will increase cloud and shower activity over the next few days, especially over the western islands. Radar imagery this morning is showing shower bands forming just south of the island chain and drifting northward into Molokai and Lanai. Some of these shower bands may drift into Oahu and Kauai later this morning.
Light large scale winds will allow local scale sea breezes to develop over each island a few hours after sunrise with clouds building over mountain and island interior sections through the day. Land breezes will form over all islands after sunset with low cloud and shower coverage decreasing for most airfields on Maui and the Big Island. Deeper tropical moisture spreading out from Kauai to Molokai will keep brief periods of MVFR conditions and showers in the forecast across the western islands through at least tonight. Isolated IFR conditions in heavy rain and thunderstorms are possible later tonight into Tuesday across the western half of the state.
AIRMET Sierra for tempo mountain obscuration remains in effect for the both Lanai and Molokai. This AIRMET may expand to Oahu and Kauai later this morning.

Marine

Low pressure north of the islands will result in continued light to gentle regional trade winds. As this low slowly moves northward the next several days, the weak pressure gradient to its south will maintain these light to gentle breezes. Weakened breezes will equate to a more calm sea state with the only lift in seas occurring from the passage of a moderate size north swell.
A moderate size, medium period north swell is peaking early this morning and will begin to slowly fade later today. Thus, the High Surf Advisory remains in effect for the north-facing shores of Niihau, Kauai, Oahu, Molokai, Maui and Big Island today. A late week northwest to north moderate, medium period swell may again increase surf along north-facing shores to near the advisory levels. A mid week arrival of a small, long period south swell may bump up south-facing shore surf during the second half of the week. Eastern shore chop will remain very small due to a lack of any significant trade flow. East-facing shores better exposed to a north swell wrap will experience an additional foot or two of surf through Tuesday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Oahu North Shore, Olomana, Maui Windward West, Kauai North, Kauai East, Koolau Windward, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.

Data Courtesy of NOAA.gov