Photo Credit: Brendan Stephen

West Kaua’i

Today: Windy. Showers and scattered thunderstorms until late afternoon, then scattered showers late in the afternoon. Some thunderstorms may produce damaging winds until late afternoon. Locally heavy rainfall possible until late afternoon. Highs around 79 near the shore to around 66 above 3000 feet. Northwest winds 25 to 30 mph with gusts to 60 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Windy. Scattered showers early in the evening, then showers likely in the late evening and overnight. Lows 62 to 68 near the shore to around 54 above 3000 feet. West winds 20 to 30 mph. Gusts up to 60 mph in the evening. Chance of rain 70 percent.

Tuesday: Windy. Partly sunny with scattered showers. Highs 79 to 84 near the shore to around 69 above 3000 feet. Northwest winds 15 to 30 mph decreasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Windy. Showers and scattered thunderstorms until late afternoon, then scattered showers late in the afternoon. Some thunderstorms may produce damaging winds until late afternoon. Locally heavy rainfall possible until late afternoon. Highs 74 to 81. West winds 20 to 30 mph with gusts to 60 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 64. West winds 20 to 25 mph. Gusts up to 45 mph in the evening. Chance of rain 50 percent.

Tuesday: Breezy. Mostly sunny with scattered showers. Highs 78 to 84. Northwest winds 10 to 20 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Windy. Showers and scattered thunderstorms until late afternoon, then scattered showers late in the afternoon. Some thunderstorms may produce damaging winds until late afternoon. Locally heavy rainfall possible until late afternoon. Highs 65 to 73 in the valleys to around 57 above 4000 feet. West winds 20 to 35 mph with gusts to 60 mph. Chance of rain near 100 percent.

Tonight: Windy. Mostly cloudy with showers likely. Lows 56 to 61 in the valleys to around 51 above 4000 feet. West winds 15 to 35 mph. Gusts up to 60 mph in the evening. Chance of rain 70 percent.

Tuesday: Windy. Partly sunny with scattered showers. Highs 68 to 76 in the valleys to around 61 above 4000 feet. West winds 10 to 30 mph shifting to the northwest 10 to 20 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Windy. Showers and scattered thunderstorms until late afternoon, then scattered showers late in the afternoon. Some thunderstorms may produce damaging winds until late afternoon. Locally heavy rainfall possible until late afternoon. Highs 68 to 78. West winds 20 to 30 mph with gusts to 60 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Windy. Scattered showers early in the evening, then showers likely in the late evening and overnight. Lows 57 to 66. West winds 15 to 30 mph. Gusts up to 60 mph in the evening. Chance of rain 70 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 71 to 81. West winds 10 to 25 mph. Chance of rain 50 percent.

East Kaua’i

Today: Windy. Showers and scattered thunderstorms until late afternoon, then scattered showers late in the afternoon. Some thunderstorms may produce damaging winds until late afternoon. Locally heavy rainfall possible until late afternoon. Highs 65 to 77. West winds 15 to 30 mph with gusts to 60 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 56 to 67. West winds 15 to 20 mph. Gusts up to 45 mph in the evening. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 69 to 81. Northwest winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Numerous showers, heavy at times, and thunderstorms will continue today as a kona storm moves through the region. Bands of strong thunderstorms are moving through islands ahead of a vigorous cold front that will sweep across the state from northwest to southeast today. These stronger thunderstorms may become severe with strong winds and the potential for hail. Strong southwesterly kona winds will increase ahead of the cold front, with the strongest wind speeds forecast for communities along the down wind north and east slopes of mountain areas. Periods of heavy rain with this storm may produce flash flooding in some areas. Weather conditions will improve over the western islands later this afternoon and evening and improve across the rest of the state by Tuesday morning. Fair weather and light winds expected from Wednesday through the weekend.

Discussion

The short range weather forecast continues to show a wet and unstable weather pattern for all islands today. Two bands of showers and thunderstorms are passing through the Hawaii Region this morning. The first band is producing numerous showers, heavy at times, with scattered thunderstorms near Maui and the Big Island. The second band is associated with the cold front and is passing eastward through Kauai and Oahu this morning. This front will continue to sweep eastward affecting all islands with increasing winds, periods of heavy showers and scattered thunderstorms ahead of the frontal trough.
Expect sustained southwest winds of 20 to 30 MPH with stronger gusts today along with periods of heavy rain and thunderstorms. These strong winds will be magnified by thunderstorms, including mountain peaks and down wind of higher elevation areas. Mountain peaks and communities along north and east slopes of mountains will see much stronger wind speeds develop as the front gets closer to each island. The timing of this cold frontal passage will vary as the front sweeps eastward. Expect the front to pass over Oahu today around 7 AM HST, Molokai and Lanai around noon HST, reaching Maui around 1 PM HST, and finally over the western Big Island around 6 PM HST.
A few of these strong thunderstorms moving over the western islands will pull down stronger winds aloft to the surface, increasing the threat for damaging and gusty winds over the islands of Niihau, Kauai and Oahu this morning. A Severe Thunderstorm Watch remains in effect for Kauai County and Oahu this morning. This threat for severe thunderstorms may move eastward to Maui County and possibly Hawaii County later today and the Severe Thunderstorm Watch may need to be expanded eastward to cover this damaging wind threat.
The potential for flash flooding will continue today for areas ahead and along the cold front. Soil moisture is already saturated from the rainfall yesterday and heavy rainfall will increase flooding potential. Periods of intense rainfall rates of 3 to 4 inches per hour today may trigger flash flooding over any island.
Tuesday and Wednesday…Well-mixed, gusty westerlies build in behind the cold front and focus showers over leeward slopes through Tuesday. Fair weather with much lighter winds are expected by Wednesday.
Thursday onward, light winds remain in the forecast lasting into the weekend. Another front could approach and stall just west of the state by Friday. Most of the moisture and instability looks to stay well north of the island chain with this next frontal band.

Aviation

A strong cold front and an upper-level trough associated with a deep low pressure system north of the main Hawaiian Islands continue to move rapidly toward the east-southeast. The front appears to be moving across Kauai early this morning, and will eventually move from Oahu to the Big Island through this afternoon. Unstable atmospheric conditions and enhanced moisture are producing widespread cloud cover and rainfall along with thunderstorms ahead of the front. This is a high impact weather event, which is very unusual for the main Hawaiian Islands. ALL aviation interests are urged to monitor the latest forecasts, and use extra caution during the next 24 hours.
Widespread MVFR conditions, and localized IFR conditions, due to low ceilings and reduced visibilities are occurring across most of the state. AIRMET Sierra remains in effect for mountain obscuration above 2 thousand feet for most islands. This AIRMET may remain in effect for most of the state into this afternoon.
The thunderstorms in the vicinity of Hawaii continue to require a convective SIGMET (XRAY series) early this morning. Note that some thunderstorms may become severe. We have also mentioned the potential for light icing occurring in clouds across most of the state in the layer from 12 to 22 thousand feet in AIRMET Zulu.
As the front continues to move down the island chain, expect significant strengthening of the low-level southwest to west winds. AIRMET Tango is currently in effect for Tempo moderate mechanical low-level turbulence below 9 thousand northwest through southeast of the higher terrain on all islands. AIRMET Tango is also in effect for sustained wind speeds of 30 kt or greater for the western islands. These strong sustained winds will likely spread to the rest of the state later today. Finally, we are including AIRMET Tango for TEMPO moderate upper-level turbulence in the layer from 18 to 30 thousand feet.

Marine

A robust cold front near Kauai will continue to move southeast across the islands tonight, bringing a wide array of marine hazards. These include the potential for gusty winds, hail and waterspouts in and around strong to severe thunderstorms, sustained near- gale to gale-force southwest to west winds, as well as rapidly increasing seas and surf. A Gale warning continues for all Hawaiian waters through this afternoon. Additionally, a High Surf Warning (HSW) for exposed north and west facing shores is in effect for a long lived northwest swell through Tuesday afternoon. Less exposed shorelines may need a High Surf Advisory (HSA), to be issued later, as the swell builds down the island chain.
Even after the front moves east of the islands, west winds are expected to remain strong to near-gale on Tuesday as low pressure moves east passing a couple hundred miles north of the islands. Winds will decline Tuesday night into Wednesday as the low departs to the northeast and a ridge builds over the area.
The strong low pushing the cold front over the islands will produce a long-lived and extra-large northwest swell that will rapidly build into the islands and bring surf heights well above High Surf Warning (HSW) levels. There is high potential for wave run- up onto vulnerable roadways and coastal areas in the HSW areas, with the most likely time for these impacts being tonight into Tuesday morning during high tide. This swell is expected to drop below warning thresholds Tuesday night into Wednesday. The northwest Pacific remains active resulting in a large northwest swell towards the end of the week near High Surf Advisory (HSA) levels. Surf along south and west facing shores will also see an increase in short- period wind waves tonight into Tuesday due to the strong onshore winds.

HFO Watches/Warnings/Advisories

Severe Thunderstorm Watch 1 until this morning for Kauai County and Oahu.
Flood Watch through late tonight for all Hawaiian Islands.
High Wind Warning until 6 PM HST this evening for all Hawaiian Islands.
High Wind Warning until 6 AM HST Tuesday for Haleakala Summit.
High Wind Warning until 6 AM HST Wednesday for Big Island Summits.
Winter Storm Warning until 6 AM HST Tuesday for Big Island Summits.
Gale Warning until 6 PM HST this evening for all Hawaiian waters.
High Surf Warning through 6 PM HST Tuesday for north and west facing shores of Niihau, Kauai, Oahu and Molokai, and north facing shores of Maui.

Data Courtesy of NOAA.gov