Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny with isolated showers. Haze. Highs around 82 near the shore to around 70 above 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows around 63 near the shore to around 52 above 3000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Haze. Highs around 83 near the shore to around 71 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny with isolated showers. Haze. Highs around 81. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows 59 to 64. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Haze. Highs around 82. Light winds. Chance of rain 20 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers. Haze. Highs 69 to 77 in the valleys to around 64 above 4000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows 52 to 57 in the valleys to around 46 above 4000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Haze. Highs 70 to 78 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 20 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Haze. Highs 74 to 81. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows 55 to 64. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Haze. Highs 75 to 82. Light winds. Chance of rain 20 percent.

East Kaua’i

Today: Mostly sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Haze through the day. Highs 74 to 81. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy with scattered showers. Haze. Lows 53 to 65. Light winds. Chance of rain 30 percent.

Tuesday: Mostly sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Haze through the day. Highs 75 to 82. Light winds. Chance of rain 30 percent.

Detailed Forecast

Synopsis

A high pressure system passing north of the islands will be replaced by a low level trough today. This means trade winds diminish and a light southeast wind pattern returns through Thursday. Sea breezes will develop over each island during the day with land breezes taking over at night. An upper level ridge over the islands will keep shower activity at isolated levels through Wednesday. Rainfall trends will increase from Thursday onward as the weather pattern becomes more unsettled. Wet weather remains in the forecast this weekend near Kauai and Oahu as a cold front moves into the western islands.

Discussion

A weak high pressure center passing by just north of the islands will be replaced by a low level trough for the next few days. Trade winds will diminish today into a light southeasterly wind pattern, placing the smaller islands from Maui to Kauai in the wind and rain shadow of the Big Island. Lighter large scale winds will allow local scale sea breezes to form over each island during the day with land breezes taking over at night.
Stable conditions under a ridge aloft and southeasterly winds will keep shower activity in the isolated to scattered range through Wednesday. Most of these showers will form over islands mountain and interior sections during the afternoon to early evening hours. Trade wind temperature inversion heights during the first half of the week will range from 5,000 to 7,000 feet indicating a drier weather pattern. These light southeasterly winds will draw volcanic emissions, vog (Volcanic smOG), from the Kilauea Volcano northward affecting all islands through Thursday.
The large scale weather pattern changes starting on Thursday with increasing shower trends as the warm and stable upper level ridge is replaced by a cold unstable upper trough. Trade wind temperature inversion heights rise to around 10,000 feet allowing deeper cumulus cloud development and the possibility for even a few thunderstorms near Kauai on Thursday night. Light winds with sea breezes and scattered to numerous showers will likely continue through Friday.
A cold front begins to approach the islands from the northwest from late Friday through Saturday. Winds will veer towards southerly directions for the western islands of Kauai and Oahu during this time period with lighter southeasterly winds expected to continue over all islands in Maui and Hawaii Counties. Southerly winds ahead of the frontal trough will pull up unstable tropical moisture and enhance showers especially along southern slopes of Kauai and Oahu from Friday night through Saturday night. Numerous showers are forecast along the cold frontal band as it moves into Kauai around midnight Sunday morning, the front then stalls near the Kauai Channel by Sunday morning with shower activity picking up over Oahu. This weather pattern favors periods of heavy rain and thunderstorm development over the western islands this weekend. However, it remains too early at this point to pin down island by island impacts. The eastern Hawaiian Islands will see moderate trade winds build back in on Sunday, with more isolated to scattered showers focused mainly over windward slopes.
Global weather models show similar unsettled weather trends for the state of Hawaii from Thursday onward. There remains some disagreement on the timing of the approaching frontal band this weekend. We blended forecast solutions from both the American (GFS) model and the European (ECMWF) model for the Saturday to Sunday forecast to smooth out errors from any one model solution. Stay tuned for updates for this weekends wet weather as forecast impacts will evolve over time.

Aviation

A weak surface ridge appears to be slightly less than 200 nm north of PHLI. The close proximity of this feature to the islands has caused the background winds to become light to locally moderate from the east-southeast near the eastern end of the state, while light and variable winds are in the vicinity of the western islands. There are scattered to locally broken low clouds and light showers moving into the north through southeast facing slopes of some of the islands early this morning. This may be resulting in brief periods of MVFR ceilings along some windward areas, but VFR conditions prevail across most of the state.
The weak background flow will allow the development of local sea breeze circulations later today. This will produce increasing cloud cover and a slight chance of showers over leeward and interior sections of most islands this afternoon. By this evening, local land breeze circulations are expected to cause most of the residual clouds and showers to diminish across these same areas.
No AIRMETs are in effect, and none are anticipated through this evening

Marine

High pressure northeast of the state will continue to weaken today, allowing the trades to ease to light to moderate levels and shift east-southeasterly near the Big Island, while becoming light and variable elsewhere. Very little change in the wind forecast is then expected through Thursday. Moderate to fresh southeast to south winds could potentially fill in ahead of an approaching front Friday through the upcoming weekend. The Small Craft Advisory (SCA) for elevated seas has been cancelled as seas have dropped below 10 feet. Winds and seas are expected to remain below SCA thresholds through Friday.
The current large northwest swell will be reinforced by a new northwest swell later today. This swell will hold through tonight, then gradually decline Tuesday and Tuesday night. The High Surf Advisory (HSA) has been extended for north and west facing shores of most of the smaller islands through 6 AM Tuesday. A couple new reinforcing northwest swells are expected Wednesday and Thursday, although surf heights should remain below advisory levels. A new large northwest swell could bring another round of advisory level surf to north and west facing shores on Friday, with a dip below advisory levels forecast for Saturday, followed by a potential warning level event on Sunday.
A small medium period south swell will continue to slowly decline today through Tuesday, with only background south swell energy expected Wednesday through Saturday. A new small long-period south swell could give south shore surf a minor boost on Sunday. East shore surf will remain small and well below normal through the upcoming weekend due to the lack of trade winds over and upstream of the islands.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.

Data Courtesy of NOAA.gov