Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Windy. Occasional showers and chance of thunderstorms. Some thunderstorms may be severe with damaging winds. Locally heavy rainfall possible. Highs 77 to 84 near the shore to around 69 above 3000 feet. Southwest winds 15 to 30 mph with gusts to 60 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows around 68 near the shore to around 59 above 3000 feet. West winds 10 to 25 mph. Gusts up to 60 mph decreasing to 50 mph after midnight. Chance of rain near 100 percent.

Friday: Mostly cloudy with numerous showers. Highs 76 to 83 near the shore to around 68 above 3000 feet. Northwest winds 10 to 15 mph. Gusts up to 50 mph in the morning. Chance of rain 60 percent.

South Kaua’i

Today: Windy. Occasional showers and chance of thunderstorms. Some thunderstorms may be severe with damaging winds. Locally heavy rainfall possible. Highs 75 to 83. Southwest winds 20 to 30 mph with gusts to 60 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows around 69. West winds 15 to 25 mph with gusts to 60 mph. Chance of rain near 100 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 75 to 82. West winds 10 to 20 mph. Gusts up to 55 mph in the morning. Chance of rain 40 percent.

Kaua’i Mountains

Today: Very windy. Occasional showers and chance of thunderstorms. Some thunderstorms may be severe with damaging winds. Locally heavy rainfall possible. Highs 72 to 78 in the valleys to around 63 above 4000 feet. Southwest winds 15 to 40 mph with gusts to 70 mph. Chance of rain near 100 percent.

Tonight: Windy. Occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 59 to 69 in the valleys to around 57 above 4000 feet. Southwest winds up to 35 mph shifting to the west 10 to 35 mph after midnight. Gusts up to 65 mph. Chance of rain near 100 percent.

Friday: Breezy. Partly sunny with numerous showers. Highs 70 to 77 in the valleys to around 61 above 4000 feet. West winds up to 25 mph with gusts to 65 mph decreasing to up to 15 mph in the afternoon. Chance of rain 60 percent.

North Kaua’i

Today: Windy. Occasional showers and chance of thunderstorms. Some thunderstorms may be severe with damaging winds. Locally heavy rainfall possible. Highs 73 to 81. Southwest winds 10 to 35 mph with gusts to 70 mph. Chance of rain near 100 percent.

Tonight: Windy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 61 to 68. Southwest winds up to 30 mph shifting to the west 10 to 20 mph after midnight. Gusts up to 70 mph. Chance of rain 90 percent.

Friday: Breezy. Mostly cloudy with numerous showers. Highs 71 to 79. West winds 10 to 20 mph. Gusts up to 65 mph in the morning. Chance of rain 60 percent.

East Kaua’i

Today: Windy. Occasional showers and chance of thunderstorms. Some thunderstorms may be severe with damaging winds. Locally heavy rainfall possible. Highs 69 to 83. Southwest winds 15 to 30 mph with gusts to 65 mph. Chance of rain near 100 percent.

Tonight: Windy. Occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 63 to 72. Southwest winds 10 to 30 mph shifting to the west after midnight. Gusts up to 60 mph. Chance of rain near 100 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 70 to 82. West winds up to 25 mph with gusts to 60 mph shifting to the northwest up to 15 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A vigorous low pressure system passing by north of the state will drag a cold front from northwest to southeast down the island chain tonight and Friday. The storm system will bring the threat for strong damaging south to southwest winds, severe thunderstorms, and flash flooding along and ahead of the front today through Friday. Conditions will gradually improve with cooler and drier air building in behind the front Friday night through the weekend. Cool and breezy trade wind weather is expected through the first half of next week.

Discussion

Currently at the surface, a vigorous area of low pressure is located around 550 miles west-northwest of Kauai, and is tracking eastward around 25 mph. Locally the winds have continued to respond overnight as the storm system moves closer, with breezy to windy conditions now present over the western islands and breezy conditions beginning to developing over Maui County. Winds are routinely gusting into the 35 to 45 mph range across Kauai and Oahu early this morning, with a peak wind gust of 58 mph reported at the Lihue Airport just after 1 AM HST. Infrared satellite imagery shows mostly cloudy conditions across most of the island chain. Radar imagery shows scattered to numerous showers moving into south facing slopes and coasts of Kauai, Maui County and the Big Island, with shower coverage more isolated over Oahu at the moment. Main forecast concerns are focused on the impacts from the significant storm system moving through the area today through Friday.
The storm northwest of the islands will intensify as it tracks steadily east-northeast today, bringing a cold front near Kauai by sunset this evening. The storm will continue to intensify as it tracks northeastward tonight and Friday, dragging the trailing cold front eastward through the island chain.
Significant impacts are expected with this system today through Friday. Strong southerly winds have developed over the western islands and will spread to Maui County later this morning. Even stronger winds will develop through the day, with very windy conditions expected across the entire state this afternoon and tonight, before winds begin to slowly diminish in strength from west to east across the island chain on Friday. A High Wind Warning is now in effect for the entire island chain through Noon Friday, with the summits of Haleakala and the Big Island holding a bit longer.
Attention then turns to the potential for severe thunderstorms later this morning through tonight. An impressively unstable airmass for this part of the world has advected northward into the islands during the past couple hours. Dewpoints have risen into the lower 70s, with the offshore buoys south of the islands now showing dewpoints in the mid 70s. This airmass will continue to be drawn northward into the state this morning on the strengthening southerly flow. 0-1 km MUCAPE values will increase into the 1500-2000 J/KG range prior to daybreak this morning, while 0-6 KM shear values rise to around 35 to 45 knots. This in combination with strong upper level support from the approach of a vigorous upper level trough as well as left front quad dynamics from a 130+ knot upper level jet should continue to increase shower coverage and intensity early this morning. Some of these thunderstorms will have the potential to producing damaging wind gusts, and with 0-3 helicity values of 150 to 300 m2/s2, waterspouts and even a few tornadoes can't be ruled out. We will continue to monitor conditions closely as a Severe Thunderstorm or Tornado Watch may be required at some point later today.
In addition, the training of thunderstorms into the islands along with intense rainfall rates will bring the potential for flash flooding. As a result, a Flood Watch remains in effect for the entire state through 6 pm Friday. A Winter Storm Warning is now in effect for the Big Island summits as heavy snow is expected to develop late today or tonight and continue into Friday night.
Weather conditions will improve from northwest to southeast down the island chain Friday and Friday night. Showery weather may hang up near the Big Island through Saturday night however as the front appears to hang up before finally pushing south of the state by early Sunday. Cooler and more comfortable conditions will gradually build in behind the front with dewpoints dropping back into the upper 50s through the weekend with north to northeast winds increasing to moderate and locally breezy levels. Cool and breezy trade wind weather appear to persist through the middle of next week, with showers confined primarily to windward and mauka areas.

Aviation

A strong low pressure system is passing north of the islands today through Friday. A strong cold front will push down the island chain through Friday. Expect conds to deteriorate towards MVFR or lower though the rest of today. Reduced flight conditions will spread across the Big Island later today. Strong southerly winds, heavy rain, and thunderstorms are possible through Friday afternoon.
AIRMET Sierra for mtn obsc is in effect for the entire island chain.
AIRMET Sierra for IFR conds is possible across the area later this morning through tonight.
AIRMET Tango is in effect for mod turb blw 100 for the entire area.
AIRMET Tango is also in effect for mod turb btn FL200 and FL420 for the entire area.
AIRMET Tango may also be needed later this morning for strong surface winds.
AIRMET Zulu remains in effect for light in-cloud icing between FL200 and FL400, with conds continuing through tonight.

Marine

A strong gale-force low pressure system will pass just N of the Hawaiian Offshore waters today and tonight, bringing the threats of strong to potentially severe thunderstorms with erratic wind gusts, gale-force sustained winds, and periods of very low visibility in heavy rain. Special Marine Warnings are likely during this time over the coastal waters due to the high potential for strong thunderstorms producing gusts above 50 kt and possibly waterspouts. A Gale Warning remains in effect for the waters around Kauai, and a Small Craft Advisory is posted for the remaining coastal waters.
Most of these weather hazards will occur in conjunction with strong and gusty S to SW winds. However, a cold front trailing south of this low center will also sweep from west to east through the islands, bringing additional heavy showers and strong thunderstorms along the frontal cloud band from tonight into Saturday. Moderate to fresh W to NW winds with improving weather trends will quickly build in after the front passes through each island. Moderate to locally strong NE trade winds will develop by Sunday as high pressure builds far NW of the islands.
The declining mid-period NNW swell will be replaced today by a larger N swell building in through Friday. This swell was generated by a gale-force low far N of the islands that set up a fetch area aimed directly at Hawaii over the last couple of days. Surf heights will build to High Surf Advisory (HSA) levels on Friday along N facing shores. The low passing N of the state will continue to intensify as it moves away from the island chain on Saturday, likely delivering a larger N swell peaking above HSA thresholds, lasting from Sunday into early next week. A couple moderate sized WNW swells are also expected, a smaller one this weekend, and a slightly larger one from Monday into Wednesday.
Rough and choppy surf, due to increasing short-period wind waves, will develop along S and W facing shores from tonight through Friday due to the increasingly strong low-level S to SW winds.

Fire weather

Critical fire weather conditions not expected through the forecast period.

HFO Watches/Warnings/Advisories

Flood Watch through Friday 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 Wind Warning until noon HST Friday for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward.
High Wind Warning from 6 AM this morning to noon HST Friday for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kona, Kohala, Big Island Interior, 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 Wind Warning from noon today to 6 PM HST Friday for Haleakala Summit.
High Wind Warning until 6 AM HST Saturday for Big Island Summits.
Winter Storm Warning from noon today to 6 AM HST Saturday for Big Island Summits.
Gale Warning until 6 AM HST Friday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.
Small Craft Advisory until 6 AM HST Friday for Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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