Photo Credit: Braden Jarvis

West Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Locally heavy rainfall possible early in the morning. Highs around 79 near the shore to around 66 above 3000 feet. West winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 65 near the shore to around 55 above 3000 feet. Northwest winds 10 to 15 mph. Chance of rain 40 percent.

Wednesday: Sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Highs around 79 near the shore to around 66 above 3000 feet. Northwest winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers until late afternoon, then isolated showers late in the afternoon. Locally heavy rainfall possible early in the morning. Highs 76 to 81. West winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers early in the evening, then scattered showers in the late evening and overnight. Lows around 63. West winds 10 to 15 mph. Chance of rain 30 percent.

Wednesday: Mostly sunny with isolated showers. Highs 76 to 81. West winds around 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Locally heavy rainfall possible early in the morning. Highs 69 to 76 in the valleys to around 59 above 4000 feet. Southwest winds up to 25 mph shifting to the west 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows 57 to 63 in the valleys to around 53 above 4000 feet. West winds up to 20 mph decreasing to up to 10 mph after midnight. Chance of rain 50 percent.

Wednesday: Mostly sunny with scattered showers. Highs 68 to 74 in the valleys to around 60 above 4000 feet. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers early in the morning, then partly sunny with isolated showers in the late morning and afternoon. Locally heavy rainfall possible early in the morning. Highs 69 to 79. Southwest winds up to 20 mph shifting to the west 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows 58 to 66. Southwest winds up to 15 mph. Chance of rain 40 percent.

Wednesday: Mostly sunny with scattered showers. Highs 69 to 79. West winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 40 percent.

East Kaua’i

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Locally heavy rainfall possible early in the morning. Highs 69 to 80. Southwest winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 57 to 68. West winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 68 to 79. Light winds becoming north up to 10 mph in the afternoon. Chance of rain 30 percent.

Detailed Forecast

Synopsis

A slow moving cold front just east of Oahu will continue to drive breezy to windy south to southwest winds today, pulling deep tropical moisture across the eastern half of the state. Unstable showers will persist over the eastern islands today into tonight, bringing periods of heavy showers and isolated thunderstorms, with enhanced rainfall potentially lingering over leeward Big Island into Wednesday. A second front is forecast to deliver another round of wet weather from Thursday through Friday.

Discussion

The cold front cleared Oahu overnight, bringing an end to any organized threat for flooding over the western islands. As a result, the Flood Watch has been cancelled for Niihau, Kauai and Oahu.
Attention now remainsfocused on Maui County where multiple bands of heavy rainfall are observed. Pockets of rain rates of 2″/hr or locally higher, especially within any thunderstorms, will be possible until the front clears Maui late this evening. Meanwhile, southerly winds at 850mb should preclude any meaningful flood threat over the Big Island until winds veer to WSW this afternoon, although pockets of heavy rainfall will still be possible. The transition to WSW flow will favor an onshore push of moisture as frontal convergence settles over the eastern end of the state. Thus, the period from roughly the 2pm to 8pm HST is forecast to mark the peak threat for flooding over the Big Island today.
Windy conditions are expected today over leeward Big Island where a Wind Advisory is in effect through 6 PM this evening. Advisory level winds are expected over the Big Island summits through 6 AM Wednesday.
Moving forward, broad cyclonic flow aloft persists as the tail end of the moisture band lingers over the eastern end of the state through at least Wednesday. Showers will therefore tend to focus in this area but will lose intensity and organization as convergence weakens in response to the departure of the parent low.
Global model consensus now keys in on renewed cyclogenesis north of the islands as the next mid-latitude trough in the sequence digs southward toward the islands on Thursday. Subsequent tightening of the gradient will bring a round of locally strong NNW winds (especially in the vicinity of Kauai and Oahu) as the attendant cold front is quickly ushered through the state Thursday-Thurs night. The accompanying band of showers will likewise move rather progressively through the forecast area and is not forecast to pose any threat for flooding. The most noteworthy impact from a sensible weather perspective will be the precipitous drop in dewpoints which, combined with gusty NNW winds will add a chill to the air. The latest GFS suggests the post frontal airmass will be characterized by dewpoints solidly in the low 50s by Friday.

Aviation

Strong south to southwesterly winds with a broad band of heavy showers will continue to slowly move across the islands in Maui County through the morning hours. Expect IFR/MVFR conditions under these heavy shower bands along with strong gusty winds and isolated thunderstorms. This heavy shower band will then move into the western Big Island later this afternoon. Strong wind gusts and showers are already developing along the Kona coast on the Big Island this morning ahead of the main heavy shower band.
AIRMET Sierra remains in effect for IFR conditions affecting Molokai and Lanai. AIRMET Sierra for tempo mountain obscuration remains in effect for Oahu and Maui. This AIRMET for mountain obscuration will likely be extended into the Big Island later this morning.
An upper level trough moving away from the state will cause the moderate upper level turbulence to diminish. AIRMET Tango for moderate turbulence between FL220-420 remains in effect through 16Z. AIRMET Tango for moderate low level turbulence below 090 remains in effect downwind of the terrain.
Light icing is also possible in layer 110 to FL220. Aviation interests are encouraged to monitor for forecast updates for the next few days as conditions will evolve.

Marine

Fresh to strong south to southwest winds ahead of a cold front located near Oahu is expected to continue moving through the islands. The parent low near 29N162W will lift north but the leading edge of the cold front as well as the prefrontal bands could bring periods of heavy rain, isolated thunderstorms, gusty winds, and the potential for waterspouts that are likely to continue today. Front will continue to track southeast through tonight as rainfall gradually diminishes over Kauai and Oahu waters. Post frontal, expect to see gentle to moderate northwest winds.
Uncertainty increases late Thursday and Friday, but forecast guidance indicates a potential for another surface low northeast of the offshore waters to develop and raise chances for another round of gusty winds and thunderstorms. An associated front will pull across the western waters Friday. This system will briefly tighten the pressure gradient across the north-northwest offshore waters enough to produce near gale force winds.
A new moderate northwest swell is still filling in on nearshore Waimea Bay PacIOOS buoy 51201 early this morning. It is expected to peak today before slowly declining Wednesday. A High Surf Advisory (HSA) has been issued for north and west facing shores of Niihau, Kauai, Oahu, and Molokai, as well as north facing shores of Maui through tonight. The slow-moving low responsible for the front has developed a fetch mainly aimed toward the western end of the island chain. The relative proximity of this source will lead to what is expected to be a large, short- lived, medium period north- northwest (330-340 degrees) swell that will build mainly over the western end of the state today too. With the enhanced southerly wind ahead of the front, and combined seas, it has met Small Craft Advisory (SCA) criteria for majority of the coastal zones that goes through tonight. The HSA and SCA may need to be extended through Wednesday but zones may need to be taken off in the afternoon package depending on observations.
Moderate to large choppy surf is expected through the end of the week but forecast confidence decreases further out in time due to the potential for the next surface low developing.
East facing shores exposed to the north swell may see an uptick in surf through the week. South facing shores will remain choppy due to the strong southwest winds Tuesday before decreasing on Wednesday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Wednesday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Kauai East, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Flood Watch through this afternoon for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, 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.
Wind Advisory until 6 PM HST this evening for Kona, Kohala.
Wind Advisory until 6 AM HST Wednesday for Big Island Summits.
Small Craft Advisory until 6 AM HST Wednesday 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, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters.

Data Courtesy of NOAA.gov