Photo Credit: Jason Weingardt

West Kaua’i

Today: Windy. Mostly cloudy with scattered showers. Highs around 82 near the shore to around 74 above 3000 feet. Northeast winds up to 30 mph increasing to 15 to 30 mph in the afternoon. Chance of rain 50 percent.

Tonight: Cloudy and breezy. Showers and isolated thunderstorms in the evening, then numerous showers and isolated thunderstorms after midnight. Locally heavy rainfall possible. Lows around 66 near the shore to around 56 above 3000 feet. Northeast winds 10 to 25 mph with gusts to 45 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 78 near the shore to around 69 above 3000 feet. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

South Kaua’i

Today: Cloudy and windy. Scattered showers early in the morning, then numerous showers in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs 79 to 84. Northeast winds 25 to 30 mph decreasing to 15 to 30 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 63 to 69. Northeast winds 15 to 25 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 78. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Cloudy and windy. Numerous showers early in the morning, then showers in the late morning and afternoon. Locally heavy rainfall possible. Highs 74 to 79 in the valleys to around 67 above 4000 feet. Northeast winds 15 to 30 mph. Chance of rain 80 percent.

Tonight: Windy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 58 in the valleys to around 51 above 4000 feet. Northeast winds 15 to 30 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Windy. Showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 69 to 74 in the valleys to around 62 above 4000 feet. Northeast winds 15 to 30 mph decreasing to 10 to 20 mph in the afternoon. Chance of rain 90 percent.

North Kaua’i

Today: Cloudy and windy. Scattered showers early in the morning, then numerous showers in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs 73 to 82. Northeast winds 15 to 30 mph. Chance of rain 70 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 59 to 67. Northeast winds 15 to 25 mph with gusts to 45 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 69 to 77. Northeast winds 15 to 25 mph. Chance of rain 90 percent.

East Kaua’i

Today: Cloudy and windy. Scattered showers early in the morning, then showers in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs 75 to 83. North winds 15 to 30 mph. Chance of rain 80 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 56 to 68. Northeast winds 15 to 25 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 70 to 78. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

A surface trough over Maui County this morning will continue to slowly drift westward through Monday, combining forces with a deepening upper level low that will enhance shower activity across the state. Periods of heavy showers and thunderstorms continue to develop along the trough over Maui County. These unstable conditions will expand slowly westward into Oahu later today and to Kauai County later tonight. The Big Island will also see increasing shower activity as deeper tropical moisture moves into the region. Strong and gusty northeast trade winds will also develop over the western islands today. Wet weather conditions will begin to improve from Monday night through Tuesday as the upper low and surface trough weaken and drift slowly westward away from the state.

Discussion

An extremely wet weather pattern continues today across most of the Hawaiian Islands today as a westward moving surface trough currently over Maui County combines forces with an upper level low deepening west of the state. Satellite imagery this morning shows deeper showers with higher and colder cloud tops over Maui and Hawaii Counties are slowly spreading westward towards Oahu. These unstable conditions continue to produce periods of heavy showers and isolated thunderstorms over Maui and Hawaii Counties this morning.
Expect increasing showers trends, heavy at times, over Oahu later today and then over the Kauai and Niihau later tonight. This wet weather pattern will continue through Monday for most islands. Therefore a Flood Watch (FFA) was extended in time through Monday afternoon for all islands except Kauai County. This FFA will likely be expanded in coverage to include Kauai and Niihau starting tonight as this wet weather pattern with heavy rainfall and thunderstorms continues to drift westward.
Deep moisture over the Big Island continues to produce significant snow and freezing rain to the summits of Mauna Kea and Mauna Loa this morning. A Winter Storm Warning was extended this morning for both Big Island Summits through Monday. Additional wintery weather and snow accumulations are expected to continue making driving conditions impassable.
Strong and gusty trade winds will also develop today between a building high pressure system northwest of Kauai and a surface trough over Maui County. A Wind Advisory was issued this morning for portions of Oahu, Kauai and Niihau lasting through this afternoon. The strongest winds in this advisory are expected over mountain areas and along leeward slopes of each island.
Medium range forecast guidance continues to improve on Tuesday and Wednesday as the surface trough and upper low will continue to weaken and drift westward away from the state. These pattern changes will produce a significant improvement in the island weather pattern with decreasing rainfall trends for all islands on Tuesday. Wind speeds will also weaken from Tuesday through Thursday as a weakening cold front approaches the islands from the north. Long range guidance continues to show a weak cold front moving from north to south through the islands by Friday morning with increasing shower trends and increasing trade winds after frontal passage. Temperatures will also cool a few degrees over all islands on Friday with a return to wet trade wind weather for next weekend.

Aviation

Early this morning, a surface trough is sustaining a large band of enhanced showers across Maui County and the Big Island. This rain has been heavy at times, particularly across Molokai and Maui where reduced visibilities and widespread MVFR ceilings have been common overnight. Over the past couple of hours, shower activity has also increased across windward Oahu and, to a lesser extent, windward Kauai as well.
The surface trough will slowly drift westward today as a low aloft deepens, shifting the focus for heavy rain westward to also include Oahu today followed by Kauai later this afternoon/early evening. Meanwhile, Maui County and the Big island will continue to experience enhanced shower activity as well. MVFR conditions and light to moderate showers can be expected to prevail at most locations, though isolated IFR conditions within heavier showers will be possible through Monday. With ample instability over the islands, isolated thunderstorms are also possible.
Gusty northeast trade winds will prevail from Kauai to Oahu through Monday. As a result, AIRMET Tango has been issued for moderate low-level turbulence downwind of the terrain of these islands. In addition, model data also suggests that moderate mid and upper level turbulence will be possible across the entire state for much of the day as convection continues. AIRMET Tango accounts for this as well.
AIRMET Sierra for mountain obscuration remains in effect for the entire islands of Maui and Molokai, as well as windward sections of Oahu and the Big Island. Mountain obscuration will likely persist through the next 24 hours, and this AIRMET may need to be expanded to include Kauai as well later today. Finally, tempo light icing will remain possible over much of the state with thick cloud cover in place.

Marine

A trough over the eastern end of the state will continue to bring rain along with the chance for thunderstorms over the coastal and offshore waters through at least Monday, and likely for waters at the western end of the state Monday night. Thunderstorm potential remains over the offshore waters through Wednesday. The trough is expected to slowly drift to the west over the next couple of days.
A surface high pressure to the northwest of the state will drift to the south today. The resultant pressure gradient between the high and the trough has caused an uptick in winds over the western waters, with Small Craft Advisory (SCA) level winds over the coastal waters near Kauai and Oahu. Winds will be a touch higher over the adjacent offshore waters. Coastal water winds should begin to decrease on Monday as the trough moves over the western end islands.
The new long-period northwest swell (310 degrees) reached the buoys to northwest of the coastal waters last evening, with a jump around 10 pm. At 2 am, buoy 51101 reported 8 feet 19 seconds. This is a bit higher than the GFS wave data, and a bit lower than the NWPS model data. The swell is expected to arrive at the Hanalei buoy shortly. The latest NWPS run shows the swell to be about a foot smaller than originally expected. The forecast for today reflects swell heights initially about 2 feet below NWPS guidance, but then catching up to NWPS guidance tonight. A complicating factor for advisory decisions for this event are the pulses of north swell that are moving into the region. The SCA has been extended through tomorrow, with an expansion into the waters near Maui County that would be exposed to the incoming swell that will raise seas in excess of 10 feet. Am holding off on issuing the High Surf Advisory for this event at this time. Forecasted surf heights for north and west facing shores are just below advisory levels for this afternoon (due to the delay in the arrival of the swell), but are currently forecasted to reach advisory levels tonight and Monday. The swell should then subside Tuesday through the rest of the week.
Surf along east facing shores will become rough over the next couple of day with the local wind swell mixes with some wrap from the north swells. Meanwhile, surf along south facing shores will remain small through Sunday, then pick up a bit Monday into Tuesday as a small, long-period south swell (190 degrees) fills in.

HFO Watches/Warnings/Advisories

Flood Watch through Monday afternoon for Oahu, Molokai, Lanai, Maui, Kahoolawe, and the Big Island.
Winter Storm Warning until 6 PM HST Monday for Big Island Summits.
Wind Advisory until 6 PM HST this evening for portions of Kauai, Niihau and Oahu.
Small Craft Advisory until 6 PM HST Monday for for waters and channels around Kauai and Oahu.
Small Craft Advisory from 6 PM this evening to 6 PM HST Monday for windward and leeward Maui waters.

Data Courtesy of NOAA.gov