Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 80 near the shore to around 68 above 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Gusts up to 45 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Windy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 near the shore to around 57 above 3000 feet. East winds up to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Wednesday: Windy. Mostly sunny with isolated showers. Highs around 79 near the shore to around 67 above 3000 feet. East winds 15 to 30 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny. Windy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79. Northeast winds 25 to 30 mph. Chance of rain 70 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows 64 to 69. Northeast winds 25 to 30 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Windy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 78. East winds 20 to 30 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Windy. Cloudy with intermittent showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 67 to 75 in the valleys to around 62 above 4000 feet. East winds 10 to 30 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy. Windy. Numerous showers in the evening, then intermittent showers after midnight. Lows 57 to 62 in the valleys to around 51 above 4000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 90 percent.

Wednesday: Windy. Cloudy with intermittent showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds 25 to 30 mph. Chance of rain 80 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 72 to 79. East winds up to 20 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 60 to 69. East winds up to 25 mph. Chance of rain 50 percent.

Wednesday: Windy. Partly sunny with scattered showers. Highs 71 to 78. East winds 15 to 30 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 79. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 70. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Windy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78. East winds 20 to 30 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A strong high pressure system located far north of the Hawaiian Islands will keep windy trade winds in the forecast into Thursday. An upper level disturbance will keep showers over windward and mountain areas through Friday with brief shower activity over leeward areas of each island. The highest rainfall trends are expected over East Maui and the windward slopes of the Big Island as an unstable upper low lingers just east of Hilo. Wind speeds may trend lower into the moderate to locally breezy range from Friday to Saturday as a cold front approaches the region from the northwest. A cold front will sweep from west to east across the island chain producing widespread showers with south to west winds on Monday.

Discussion

Water vapor satellite imagery highlights a narrow upper level trough over the islands with an unstable upper low anchoring just east of the state. Isolated thunderstorms are developing around this low pressure system and will drift into windward Maui and the Big Island later today through Wednesday. Expect periods of wet weather affecting all island into Saturday. A strong 1038 MB high pressure system remains far north of the state, producing strong and gusty trade winds across the Hawaii region through Thursday. Upper air weather balloon soundings at 2 AM HST (12Z) from Hilo and Lihue show trade wind temperature inversion heights ranging from 7,000 to 10,000 feet this morning.
Strong easterly surface winds converging over island mountains will combine forces with instability under the upper level trough producing periods of showers across the windward and mountain areas. Trade wind temperature inversion heights will remain in the 7,000 to 10,000 foot range into Saturday keeping wet weather trends in the forecast for all islands. The high pressure center far north of the islands will slowly weaken over the next few days with decreasing wind trends into the moderate to locally breezy range from Friday into Saturday, with winds becoming light and variable on Sunday ahead of an approaching cold front. However, this high will remain strong enough to produce windy trade winds into Thursday with wind advisories over land, and small craft advisories to gale warnings over windier coastal waters. A Wind Advisory remains in effect through Wednesday afternoon for the windier areas of most islands.
An upper level low will continue to deepen, and dig in just east of the Big Island through Wednesday. An upper level short wave trough rotating around this system will enhance shower activity over all islands through the morning hours. The highest rainfall amounts over the next few days will likely fall over windward slopes of Maui and the Big Island, as these islands are closer to the unstable cold core of this upper low. Brief periods of icy conditions may reach the Maui and Big Island summits around and above the 10,000 foot elevation level during the overnight hours through Wednesday as temperatures hover at or below freezing.
In the long range forecast for the upcoming weekend, wind speeds will decrease and becoming light and variable on Sunday as a cold front approaches the islands from the northwest. Shower activity will also trend lower over the smaller islands with continued higher rainfall activity over East Maui and the windward Big Island into the weekend. Both the American (GFS) and the European (ECMWF) extended range guidance shows a cold front sweeping widespread rain with southerly winds spreading from west to east across the island chain on Monday. Stay tuned for updates in this extended range forecast as this weather pattern will evolve over time.

Aviation

Strong high pressure north of the islands will keep strong and gusty trade winds in place during the next couple days. Clouds and showers will favor windward and mauka areas, but a few will reach leeward communities at times. Some MVFR cigs/vsbys can be expected in the passing showers, with showers most prevalent over windward slopes and coasts, particularly over the eastern end of the state.
AIRMET Sierra remains in effect for mountain obscuration over windward sections of most islands. This AIRMET will likely remain in place through the morning hours, with some improvement possible over windward sections of Kauai and Oahu this afternoon.
AIRMET Tango remains in effect for moderate to isolated severe low level turbulence over and downwind of the terrain of all islands. AIRMET Tango is also in effect for strong surface winds across the entire state.

Marine

Rough conditions out across the waters will continue into the second half of the week as strong high pressure (1038 mb) remains positioned to the north. Overnight satellite data showed 25-35 kt winds with seas hovering in the 10-15 ft range, which line up well with buoy observations at the PacIOOS Mokapu station and a drifter buoy east of Hilo this morning. Guidance supports this and depicts a large belt of strong northeast to east trades over and upstream of the state continuing. Gales will continue through midweek over the windier waters and channels of Maui County and the Big Island. For the extended, a pattern transition is likely this weekend as a cold front approaches, which means a break in the strong winds/seas.
Surf along east facing shores will build today, with heights surging toward the warning threshold of 15 ft (faces) tonight through Wednesday due to the aforementioned winds over and upstream of the state. A downward trend is expected Friday through the upcoming weekend as the ridge weakens and winds ease.
Surf along north facing shores will remain well below the seasonal average each day through next weekend. Satellite data showed a large swath of gales aimed at the area down the 310 degree directional band associated with a system tracking eastward toward the Date Line. This supports a small west-northwest swell arriving Friday, then lingering into the weekend.
Surf along south facing shores will remain near the seasonal average each day, with mainly wind swell wrapping into exposed areas.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST Wednesday for most Hawaiian Islands.
High Surf Advisory until 6 PM HST Thursday for east facing shores of Kauai Oahu Molokai Maui and the Big Island.
Small Craft Advisory until 6 PM HST Thursday for most Hawaiian coastal waters.
Gale Warning until 6 PM HST Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov