Photo Credit: Braden Jarvis

West Kaua’i

Rest Of Today: Partly sunny early in the morning then becoming cloudy. Scattered showers and isolated thunderstorms early in the morning, then showers and isolated thunderstorms in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs around 82 near the shore to around 70 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 90 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 67 near the shore to around 56 above 3000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Wednesday: Cloudy and breezy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Highs around 82 near the shore to around 70 above 3000 feet. East winds up to 20 mph. Chance of rain 70 percent.

South Kaua’i

Rest Of Today: Partly sunny early in the morning then becoming cloudy. Scattered showers and isolated thunderstorms early in the morning, then showers and isolated thunderstorms in the late morning and afternoon. Locally heavy rainfall possible in the late morning and afternoon. Highs around 79. South winds up to 15 mph. Chance of rain 80 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 63 to 68. Northeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 90 percent.

Wednesday: Cloudy and breezy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Highs around 79. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Rest Of Today: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible in the late morning and afternoon. Highs 69 to 76 in the valleys to around 60 above 4000 feet. Light winds. Chance of rain 90 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 56 to 61 in the valleys to around 49 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 90 percent.

Wednesday: Cloudy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Highs 69 to 76 in the valleys to around 60 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Rest Of Today: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible in the late morning and afternoon. Highs 72 to 82. Light winds. Chance of rain 90 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 59 to 67. Southeast winds up to 15 mph. Chance of rain 90 percent.

Wednesday: Cloudy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Highs 72 to 82. Southeast winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Rest Of Today: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible in the late morning and afternoon. Highs 72 to 81. South winds up to 10 mph. Chance of rain 90 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 56 to 69. Northwest winds up to 10 mph shifting to the northeast after midnight. Chance of rain 90 percent.

Wednesday: Cloudy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Highs 72 to 81. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Detailed Forecast

Update

Recent nearshore buoy observations indicate the northwest swell coming in higher than predicted, so a High Surf Advisory has been issued for north and west facing shores of Niihau, Kauai, Oahu and Molokai, as well as north facing shores of Maui through early Wednesday morning.

Synopsis

Light to moderate winds are blowing from the east to southeast direction across the Hawaiian Islands this morning as an approaching low and weakening cold front breaks down the ridge north of the islands. Showers and isolated thunderstorms are possible over the northwestern islands and the Big Island in a southeast wind pattern through Wednesday. The high pressure ridge builds back in north of the region by late Wednesday with strengthening trade winds in the breezy to locally windy range lasting into the weekend. Passing showers will trend back to the typical windward and mountain areas from Wednesday afternoon onward.

Aviation

A weakening frontal boundary located slightly more than 250 nm northwest of Kauai is causing the winds to be from the southeast near the western islands, while east-southeast winds are in the vicinity of Maui and the Big Island. An upper-level low is also developing far northwest of Kauai. This feature is causing instability to increase across the region, especially over the western islands. These unstable atmospheric conditions combined with deep moisture will likely allow clouds and showers with a slight chance to develop over the far western end of the island chain through this morning. Brief periods of MVFR conditions are possible in clouds and showers along east through southeast facing sections this morning, especially on Kauai. VFR conditions will likely prevail elsewhere this morning.
Local sea breezes will likely develop over each of the individual islands later today. At the same time, the proximity of the upper-level low to the state may cause additional instability over the state. This will likely allow clouds with embedded showers and a slight chance of thunderstorms to form over most of the state by this afternoon. Expect periods of MVFR conditions at times in clouds and showers, with isolated IFR conditions possible with the heaviest downpours or thunderstorms.
AIRMET Sierra for mountain obscuration remains in effect for Kauai. We will monitor observations to determine if this AIRMET needs to be continued later today. This AIRMET may also be needed for additional islands, such as Oahu, later today.

Marine

A weak cold front slowly approaching the islands from the northwest will weaken veering east to southeast winds to more moderate magnitudes through the middle of the week. Winds will remain below Small Craft Advisory thresholds within the typically windy waters surrounding Maui County and Big Island through tonight. More areal wide moderate to locally strong trade winds will return by Thursday and persist into next weekend as surface high pressure moves north of the state.
A moderate size, long to medium period northwest swell (310 degree) has been filling in around the islands. This will lift surf along the north and west-facing shores as this swell peaks and then levels out through the morning. Surf will near High Surf Advisory (HSA) levels today before beginning its decline Wednesday. Small surf along south-facing shores will slowly increase this week as two small, long period south southwest swells (180-200 degree) build into the region Wednesday and again this weekend. This south swell energy may peak Wednesday's south shore surf to near or just under HSA heights. East chop will remain small through Wednesday as the region remains under light east or southeast breezes in response to an approaching weak front. East-facing wind wave conditions will slightly trend up later this week as the trades return and restrengthen over and upstream of the islands.

Prev discussion

/ISSUED 346 AM HST Tue May 2 2023/
The satellite imagery this morning continues to show a low pressure system roughly 600 miles northwest of Kauai moving towards the Hawaiian Islands. Thunderstorms and shower bands are developing ahead of a weakening cold front. Local radar imagery from Kauai shows slow moving heavy rain and thunderstorms are already developing in the southern Kauai channel this morning. Heavy showers and thunderstorms from the instability surrounding this low will likely develop over Kauai today and light to moderate southerly winds will result in slow moving storm cells.
As this low drifts closer to the islands today it will become cut off from the mid latitude westerly winds and the cold front ahead of the system will weaken into a trough. This low pressure area will continue to weaken the ridge north of the state, producing light to moderate southeast winds across the Hawaii region through Wednesday. The forward motion of this low will slow as the forward movement on the trough stalls out a few hundred miles northwest of Kauai by this afternoon. The system will then slowly drift westward on Wednesday and Thursday.
Unstable conditions over the northwestern Hawaiian Islands will produce slow moving enhanced showers over the islands of Kauai, Niihau and Oahu along with isolated thunderstorms. The highest rainfall amounts are forecast over the islands in Kauai County due to the closer proximity to the approaching low and converging unstable shower bands. Heavy rainfall showers and thunderstorms will develop over Kauai and Niihau today and a Flood Watch was issued for Kauai and Niihau through early Wednesday morning due to slow moving heavy rain and thunderstorms increasing the flash flooding threat.
Shower activity over the Big Island through Wednesday will shift to the east and southeast slopes, and over interior sections from converging southeasterly winds and sea breezes. The islands in Maui County will fall into the lee side rain shadow of the Big Island through the first half of the week, decreasing rainfall potential. Sea breezes will develop over the western slopes of each island due to day time heating. Sea breeze convergence areas and island heating may produce brief showers over leeward island mountains and interior sections. Oahu may see some shower enhancement today as the sea breezes, surface heating, and instability combine forces to increase afternoon to evening shower activity. Shower activity may trend lower for all islands on Wednesday as the instability associated with the cut off low begins to drift westward away from the state and trade winds begin to return.
From Wednesday afternoon through Sunday, the pattern will shift back to more typical breezy to locally windy trade wind weather pattern as the subtropical ridge north of the state builds back in. Clouds drifting along in the trade winds will be lifted over windward mountain ranges, producing passing showers along windward and mountain areas through the weekend. The highest shower coverage will develop mainly from the overnight to early morning hours.
AVIATION… A weakening frontal boundary located slightly more than 250 nm northwest of Kauai is causing the winds to be from the southeast near the western islands, while east-southeast winds are in the vicinity of Maui and the Big Island. An upper-level low is also developing far northwest of Kauai. This feature is causing instability to increase across the region, especially over the western islands. These unstable atmospheric conditions combined with deep moisture will likely allow clouds and showers with a slight chance to develop over the far western end of the island chain through this morning. Brief periods of MVFR conditions are possible in clouds and showers along east through southeast facing sections this morning, especially on Kauai. VFR conditions will likely prevail elsewhere this morning.
Local sea breezes will likely develop over each of the individual islands later today. At the same time, the proximity of the upper-level low to the state may cause additional instability over the state. This will likely allow clouds with embedded showers and a slight chance of thunderstorms to form over most of the state by this afternoon. Expect periods of MVFR conditions at times in clouds and showers, with isolated IFR conditions possible with the heaviest downpours or thunderstorms.
AIRMET Sierra for mountain obscuration remains in effect for Kauai. We will monitor observations to determine if this AIRMET needs to be continued later today. This AIRMET may also be needed for additional islands, such as Oahu, later today.
MARINE… A weak cold front slowly approaching the islands from the northwest will weaken veering east to southeast winds to more moderate magnitudes through the middle of the week. Winds will remain below Small Craft Advisory thresholds within the typically windy waters surrounding Maui County and Big Island through tonight. More areal wide moderate to locally strong trade winds will return by Thursday and persist into next weekend as surface high pressure moves north of the state.
A moderate size, long to medium period northwest swell (310 degree) has been filling in around the islands. This will lift surf along the north and west-facing shores as this swell peaks and then levels out through the morning. Surf will near High Surf Advisory (HSA) levels today before beginning its decline Wednesday. Small surf along south-facing shores will slowly increase this week as two small, long period south southwest swells (180-200 degree) build into the region Wednesday and again this weekend. This south swell energy may peak Wednesday's south shore surf to near or just under HSA heights. East chop will remain small through Wednesday as the region remains under light east or southeast breezes in response to an approaching weak front. East-facing wind wave conditions will slightly trend up later this week as the trades return and restrengthen over and upstream of the islands.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight for Niihau, Kauai,
High Surf Advisory until 6 AM HST Wednesday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.

Data Courtesy of NOAA.gov