Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly cloudy. Scattered showers and isolated thunderstorms early in the morning, then scattered showers and chance of thunderstorms in the late morning and afternoon. Highs around 83 near the shore to around 73 above 3000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 68 near the shore to around 54 above 3000 feet. Light winds. Chance of rain 30 percent.

Saturday: Partly sunny with scattered showers. Highs around 83 near the shore to around 73 above 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Scattered showers and isolated thunderstorms early in the morning, then scattered showers and chance of thunderstorms in the late morning and afternoon. Highs around 81. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 67. Light winds. Chance of rain 40 percent.

Saturday: Partly sunny with scattered showers. Highs around 81. East winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Scattered showers in the morning. Chance of thunderstorms through the day. Showers likely in the afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs around 76 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 57 in the valleys to around 49 above 4000 feet. Light winds. Chance of rain 50 percent.

Saturday: Mostly cloudy with showers likely. Highs around 76 in the valleys to around 65 above 4000 feet. East winds around 10 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly cloudy. Scattered showers and isolated thunderstorms early in the morning, then showers likely and chance of thunderstorms in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs 76 to 82. Light winds. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 57 to 66. Light winds. Chance of rain 50 percent.

Saturday: Mostly cloudy with scattered showers. Highs 76 to 82. East winds around 10 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Scattered showers and isolated thunderstorms early in the morning, then showers likely and chance of thunderstorms in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs 74 to 80. Light winds. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 55 to 68. Light winds. Chance of rain 40 percent.

Saturday: Mostly cloudy with scattered showers. Highs 74 to 80. East winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The threat for strong to severe thunderstorms and heavy rainfall will continue across the state through tonight as a strong upper level disturbance settles southward into the area. Although the thunderstorm potential will lower early next week, plenty of moisture lingering combined with afternoon sea breezes and a broad surface trough nearby will support afternoon showers over interior and leeward areas each day. The wet pattern could continue through the latter half of next week as another upper disturbance approaches.

Discussion

The morning water vapor imagery showed broad upper troughing over the region with a strong shortwave trough digging southeastward into the area. The surface trough has responded to the upper height falls and strengthened near Kauai overnight. High- resolution model guidance reflects this, with some depicting a mesoscale low forming along the trough today. MUCAPES of 1000 to 2000 J/Kg combined with effective deep layer shear values of 35 to 45 knots will support a few strong to severe thunderstorms and locally heavy rainfall that could lead to flash flooding into Saturday.
Low-level convergent flow into this surface trough will be the focus for heavy showers and thunderstorms through daybreak this morning across the smaller islands, mostly impacting the nearshore coastal waters initially. In addition to this activity over the waters, this flow is translating to heavy showers anchoring in some island terrain, particularly over the Koolaus and windward areas of Oahu and on Maui near Hana. Peak rainfall totals are closing in on 7 inches in the past 24-Hrs (as of 2 AM HST) along the Koolaus, which has led to rapid water level rises in the Waiahole/Waikane streams. With the next round of heavy showers lifting northward toward these areas on Oahu, the potential for flash flooding will be the main concern through daybreak, which includes the peak morning commute times. A transition to more of a widespread/statewide potential is possible today through tonight as the upper low and surface reflection drift eastward across the area. As a result, a Flood Watch remains in effect for the entire state.
Guidance shows the upper low beginning to weaken as it lifts off to the northeast later this weekend into early next week, which will support a diminishing likelihood of thunderstorms. The rainfall chances, however, will likely linger as the aforementioned broad surface trough remains over or nearby to the west Sunday through next week. Expect the light to moderate east to southeast low-level flow to persist, which will allow the land and sea breeze regime to hold for most areas. This combined with a sufficient amount of moisture will keep the rainfall chances up each day, especially through the afternoon and early evening periods over interior/leeward areas with the sea breezes. The wet pattern could persist through the second half of the week as another upper low drops southward into the area drawing up deep tropical moisture and southerly flow over the state.

Aviation

A broad surface trough and upper level disturbance will slowly move south across the state today. This will bring enhanced shower activity along with the threat of a few thunderstorms. Thunderstorm activity will be greatest over western islands this morning then slowly shift southeastward later today. Expect periods of MVFR conditions as showers move through, with occasional IFR possible under heavier showers.
AIRMET Sierra remains in effect for tempo mountain obscuration across the smaller islands and windward sections of the Big Island, with little change expected today.
AIRMET Tango may become necessary for moderate mid to upper level turbulence as the upper level disturbance moves across the state.
AMD NOT SKED for PMDY continues due to equipment issues, with no timeline for restoration.

Marine

An upper disturbance moving into the area from the north will keep the threat of strong, possibly severe, thunderstorms in the forecast through Saturday. These thunderstorms may produce dangerous wind gusts, hail, and frequent lightning. A trough near Kauai will strengthen and expand across the island chain today, then linger through the weekend. As a result, light and variable winds will replace the usual trade wind flow at the surface today and Saturday. Light to moderate easterly trade winds will return starting Sunday.
A long-lived south swell will affect the islands into the weekend. Surf along south facing shores is expected to remain at the High Surf Advisory threshold of 10 feet through this afternoon, then gradually decline Saturday through Tuesday. A series of overlapping long- period south swells will give another sizable boost to south shore surf Wednesday through late next week. This event represents the most sustained south swell of the year.
North shore surf will remain tiny through this morning. A small reinforcing short-period north-northwest swell will build in this afternoon and continue through the weekend. A small long- period northwest swell will build Sunday night, giving north shore surf a boost early next week. Surf along east facing shores will be well below normal levels through the middle of next week.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight 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 PM HST this evening for Niihau, Kauai Leeward, Waianae Coast, Kahoolawe, Maui Leeward West, Kona, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Molokai Leeward South, Lanai Leeward, Lanai South, Maui Central Valley South, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast.
High Wind Warning from 6 AM this morning to 6 AM HST Saturday for Big Island Summits.
Winter Storm Warning from noon today to 6 AM HST Saturday for Big Island Summits.

Data Courtesy of NOAA.gov