West Kaua’i

Today: Breezy. Occasional showers. Locally heavy rainfall possible. Highs around 80 near the shore to around 67 above 3000 feet. Northeast winds up to 10 mph shifting to the southeast up to 20 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Locally heavy rainfall possible. Lows around 68 near the shore to around 60 above 3000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Tuesday: Windy. Mostly cloudy with showers likely. Locally heavy rainfall possible. Highs around 81 near the shore to around 68 above 3000 feet. East winds 10 to 30 mph. Gusts up to 50 mph in the morning. Chance of rain 70 percent.

South Kaua’i

Today: Breezy. Occasional showers. Locally heavy rainfall possible. Highs 73 to 80. Northeast winds 10 to 15 mph shifting to the east up to 20 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Locally heavy rainfall possible. Lows around 69. East winds 15 to 20 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Cloudy with occasional showers. Locally heavy rainfall possible. Highs 74 to 81. East winds 10 to 20 mph. Chance of rain 90 percent.

Kaua’i Mountains

Today: Breezy. Occasional showers. Locally heavy rainfall possible. Highs 67 to 74 in the valleys to around 60 above 4000 feet. East winds up to 10 mph increasing to up to 25 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Windy. Occasional showers. Locally heavy rainfall possible. Lows 61 to 67 in the valleys to around 57 above 4000 feet. East winds 15 to 30 mph. Chance of rain near 100 percent.

Tuesday: Windy. Cloudy with occasional showers. Locally heavy rainfall possible. Highs 68 to 75 in the valleys to around 60 above 4000 feet. East winds 15 to 35 mph decreasing to 10 to 25 mph in the afternoon. Chance of rain 90 percent.

North Kaua’i

Today: Breezy. Occasional showers. Locally heavy rainfall possible. Highs 70 to 79. Southeast winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Locally heavy rainfall possible. Lows 62 to 70. East winds 10 to 25 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Mostly cloudy with showers likely. Locally heavy rainfall possible. Highs 71 to 80. East winds 10 to 25 mph. Chance of rain 70 percent.

East Kaua’i

Today: Breezy. Occasional showers. Locally heavy rainfall possible. Highs 67 to 78. East winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Locally heavy rainfall possible. Lows 62 to 73. East winds 15 to 25 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Cloudy with occasional showers. Locally heavy rainfall possible. Highs 66 to 79. East winds 10 to 25 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

A surface trough west of Kauai and its parent upper level low will sag southward today. This will continue the threat of flash flooding into Tuesday. Breezy east-southeast winds will strengthen to breezy to windy levels today which may require a Wind Advisory for lower elevations along ridges and points. Significant snow and ice accumulations will continue for the Big Island Summits today. The upper level low is expected to weaken today into Tuesday as the surface trough shifts west of the state, allowing chances of thunderstorms and heavy rain to taper off. Cloudy conditions will still continue through the rest of the week as light winds develop during the second half of the week allowing for sea breezes to develop but showers will only be light to moderate.

Discussion

Latest satellite imagery shows a thick band of clouds with embedded heavy showers and thunderstorms mainly over the western offshore and Kauai coastal waters. High clouds from the upper level low are streaming over the state from the subtropical jet. Numerous low level clouds and moderate to locally heavy showers are focused along southeast and eastern slopes of the Big Island, with scattered clouds and isolated moderate to brief heavy showers developing elsewhere along southeast and eastern slopes of the island chain.
The statewide Flood Watch remains in effect through this afternoon, and may need to be extended into Tuesday for all or portions of the state. Latest near-term model guidance shows the the greatest potential for excessive rain and flooding to occur over Kauai County and along southeast and eastern exposures of Big Island and Maui County today and tonight. However the convective nature of this pattern will still keep some potential of heavy rain and thunderstorms over the rest of the state.
Heavy snow and icy conditions will continue for the Big Island Summits through today. In addition, winds are expected to ramp up to boarderline High Wind Warning Criteria later this afternoon. Thus, a High Wind Warning and a Winter Storm Warning remain in effect through to 6 AM HST Tuesday.
Strengthening southeast winds today could warrant the issuance of a Wind Advisory for low-level elevations along ridges and peaks. Will continue to monitor all available observations throughout the day.
The threat of heavy rain and thunderstorms will drastically decrease Tuesday as the upper level low weakens and the surface trough shifts west of the state. Southeast winds will also gradually ease Tuesday through Wednesday to light to breezy levels. Weather conditions will continue to remain somewhat unsettled through Wednesday due to the weakening upper level low still lingering near the state. Low level winds will continue to remain out of the east to southeast direction, which will continue to favor showers over windward Big Island and possible Kauai. Some locally heavy showers will continue to remain possible on Wednesday. Starting Thursday, a front passing north of the state will cause the winds to weaken and veer further to the southeast direction. With the light winds in place on Thursday, we could see sea breezes develop during the day, which will allow for afternoon clouds and scattered showers. Overall, conditions should be stabilizing on Thursday which should keep any showers on the lighter side.
From Friday and beyond, there is still quite a bit of uncertainty in the long range forecast. Both the GFS and ECMWF show an area of low pressure developing north of the state, but they differ in location and intensity. The global ensemble members seem to favor showers over the western half of the state. For now the forecast reflects scattered showers over the western half of the state, but we could see shower coverage increase depending on the development of the low. Beyond Saturday, long range models are showing a cold front pushing through the state early next week.

Aviation

Unsettled weather will continue to impact primarily windward and mauka areas today and tonight. Period of MVFR and/or IFR conditions will impact these area, while primarily VFR conditions prevail in leeward areas. Easterly trade winds will increase across the islands today, becoming breezy and gusty in most areas this morning.
AIRMET Sierra remains in effect for mountain obscuration over windward areas of all islands. These conditions will likely persist through the day. AIRMET Tango remains in effect for mid to upper level turbulence, which will likely persist for much of the day as well. AIRMET Zulu is also in effect for light to moderate rime icing across the entire state.

Marine

A trough west of the offshore waters will continue to bring scattered to numerous showers and isolated thunderstorms to the coastal waters through mid-week. Strong to locally gale force winds will hold through Tuesday, then begin to weaken. A Gale Warning remains in effect for the Alenuihaha Channel through early Tuesday. A Small Craft Advisory for both winds and seas remains in effect for the remaining waters through at least Tuesday evening.
A moderate, medium period, north northeast (020-030 degree) swell will veer to a more east northeasterly direction through Tuesday. Therefore, moderate surf along north facing beaches is expected to decline. The next small, long period, northwest (310 degree) swell will build late Tuesday and hold through Friday.
An easterly wind fetch generated by lowering pressures south and west of the islands will significantly increase easterly wind wave swell through early Wednesday. This east swell will impact most eastern facing shores of all islands. Thus, a High Surf Advisory will remain in effect for all east-facing shores through early Wednesday morning.
The Coastal Flood Statement will continue through late tonight. Expect minor flooding of low lying coastal areas during the early morning high tides.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
High Surf Advisory until 6 AM HST Wednesday for Olomana, Kauai East, Kauai South, East Honolulu, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, South Haleakala, Big Island Southeast, Big Island East, Big Island North.
Winter Storm Warning until 6 AM HST Tuesday for Big Island Summits.
High Wind Warning until 6 AM HST Tuesday for Big Island Summits.
Small Craft Advisory until 6 PM HST Tuesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Warning until 6 AM HST Tuesday for Alenuihaha Channel.

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Data Courtesy of NOAA.gov