Photo Credit: Pamela Goguen Lynch

West Side

Today: Isolated showers after 10am. Mostly sunny, with a high near 82. East northeast wind 5 to 8 mph becoming calm. Chance of precipitation is 20%.

Tonight: Isolated showers. Partly cloudy, with a low around 61. East wind 3 to 8 mph. Chance of precipitation is 20%.

Tuesday: Isolated showers. Mostly sunny, with a high near 82. Light and variable wind becoming south around 6 mph in the afternoon. Chance of precipitation is 20%.

South Side

Today: Isolated showers after 10am. Mostly sunny, with a high near 82. Light and variable wind becoming east 8 to 13 mph in the afternoon. Chance of precipitation is 20%.

Tonight: Scattered showers. Partly cloudy, with a low around 59. East wind 9 to 13 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Isolated showers. Mostly sunny, with a high near 82. East wind 5 to 9 mph becoming calm in the afternoon. Chance of precipitation is 20%.

North Shore

Today: Isolated showers before 10am. Sunny, with a high near 80. Breezy, with a northeast wind 9 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Partly cloudy, with a low around 60. Breezy, with an east southeast wind 10 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 20%.

Tuesday: Isolated showers. Mostly sunny, with a high near 80. East southeast wind 5 to 10 mph becoming light and variable in the afternoon. Chance of precipitation is 20%.

Central Maui

Today: Scattered showers, mainly after 11am. Mostly sunny, with a high near 80. North northeast wind 6 to 9 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 58. East wind 9 to 11 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Scattered showers, mainly before 7am. Mostly sunny, with a high near 80. East wind around 7 mph. Chance of precipitation is 40%.

Upcountry

Today: Scattered showers after 10am. Mostly sunny, with a high near 67. Light and variable wind becoming east 5 to 9 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Isolated showers. Partly cloudy, with a low around 49. East southeast wind 8 to 10 mph. Chance of precipitation is 20%.

Tuesday: Isolated showers. Mostly sunny, with a high near 67. East southeast wind 5 to 8 mph becoming light and variable in the afternoon. Chance of precipitation is 20%.

East Maui

Today: Scattered showers. Partly sunny, with a high near 78. East southeast wind 7 to 11 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely, mainly after 7pm. Mostly cloudy, with a low around 56. Breezy, with an east southeast wind around 16 mph, with gusts as high as 22 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Showers likely, mainly before 7am. Partly sunny, with a high near 78. Breezy, with an east southeast wind 13 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Lanai City

Today: Scattered showers after 10am. Mostly sunny, with a high near 74. Calm wind becoming east northeast 5 to 7 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Partly cloudy, with a low around 62. East wind 3 to 8 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Isolated showers. Mostly sunny, with a high near 74. Light and variable wind becoming south 5 to 9 mph in the afternoon. Chance of precipitation is 20%.

Kaunakakai

Today: Isolated showers after 10am. Mostly sunny, with a high near 79. Breezy, with an east wind 10 to 15 mph, with gusts as high as 20 mph. Chance of precipitation is 20%.

Tonight: Scattered showers. Partly cloudy, with a low around 66. Breezy, with an east wind 10 to 15 mph becoming light after midnight. Winds could gust as high as 20 mph. Chance of precipitation is 30%.

Tuesday: Scattered showers, mainly before noon. Mostly sunny, with a high near 79. Light and variable wind becoming south around 6 mph in the afternoon. Chance of precipitation is 30%.

Detailed Forecast

Synopsis

The high pressure system north of the islands will slowly drift eastward as a cold front moves in from the west. Easterly trade winds will diminish today, and veer to the southeastly and southerly direction by Tuesday ahead of an approaching cold front. A cold front will sweep from west to east down the island chain from Tuesday night through Thursday morning. Clouds and showers along the frontal band will produce widespread rain, heavy at times, with a few thunderstorms. Colder air behind the front will bring drying trends with below normal temperatures spreading across the islands from Wednesday into the weekend.

Discussion

Satellite imagery this morning shows a high pressure system sandwiched between a cold front moving into the Pacific Northwest and another cold front moving into the Hawaii region from the west. Low level cloud bands, likely unstable remnants of an old frontal boundary, are drifting in on the trade winds from east to west. Radar imagery shows scattered to numerous showers moving into windward and mountain areas this morning. A cold front, roughly 1000 miles northwest of Kauai, continues to move into the Central Pacific region from the west. This cold front will pass through the islands later this week spreading widespread rainfall across the state. A weak jet stream north of Hawaii will produce some ice crystal cirrus clouds today enhancing sunrise and sunset colors.
Easterly trade winds will diminish today as the high pressure system north of the islands drifts further eastward away from the state. A cold frontal system will move into the region from the west causing wind directions to veer southeasterly and southerly tonight through Tuesday. Numerous shower activity favoring windward and mountain areas will also diminish by Tuesday morning, as the wind directions shift to a more southerly direction. Prefrontal shower bands will develop on Tuesday producing brief periods of showers moving up over the islands from a southerly direction. The cold front will begin spread showers into Kauai by Tuesday night.
On Wednesday, a fast moving cold front sweeps through the Hawaiian Islands from west to east. Southwest winds will develop ahead of the front, quickly shifting to a cool and breezy northwesterly winds after the front passes each island. Widespread rainfall will develop along the frontal band with showers, heavy at times, spreading across all islands in the state. Enough instability will develop with this system for a few thunderstorms along and ahead of the frontal cloud band. The latest models are showing a prefrontal convergence band of showers developing just 6 to 12 hours ahead of the cold frontal boundary, producing two rounds of showers adding to storm total rainfall amounts for each island. The initial timing on the cold frontal passage starts with Kauai and Niihau from Tuesday night to Wednesday morning, reaching Oahu by Wednesday afternoon, moving into Maui County from Wednesday afternoon to evening, and finally drifting into the Big Island from Wednesday night to Thursday morning. Snow levels will drop to around 11,000 feet elevation on Wednesday with snowfall likely for the highest summits of Mauna Kea and Mauna Loa on the Big Island. Get your jackets ready, as much colder air will move into the islands behind the front with high and low temperatures falling below normal into the weekend.
The cold front will move fairly rapidly from west to east through the state this week decreasing statewide flooding threats. However, small scale heavy rain bands within this system may line up over individual islands keeping a possibility for more localized flash flooding in the forecast. For now, our confidence is not high enough to issue Flash Flood Watches for any islands at this time. We will continue to monitor this rainfall event closely with regular forecast updates as the weather situation evolves.
On Thursday and Friday, more stable northerly flow will develop over the islands on Thursday as the front moves eastward away from the state. Much colder temperatures are forecast with highs for most locations near sea level falling into the mid to upper 70’s and the overnight temperatures falling into the low 60’s. Even colder temperatures are forecast for higher elevation communities. Moderate northeasterly trade winds return from Thursday night to Friday with isolated to scattered showers.
Saturday and Sunday, moderate to breezy northeasterly trade winds continue on Saturday. Trade winds may weaken on Sunday as a low pressure system drifts into the region from the east. Long range forecast guidance remains poor between the American and European models on the movement and intensity of this low. However, we continue to have a high confidence in below normal temperatures lasting through Sunday.

Aviation

A surface high far north of the islands will produce moderate to fresh easterly trade winds today. Winds will slowly weaken and veer out of the southeast over the next 24 hours as a front approaches. VFR conditions will prevail today, with isolated MVFR ceilings and visibilities over east sections.

Marine

No significant changes to the forecast this morning. Winds remain just below Small Craft Advisory (SCA) levels over the windier waters, and winds are expected to trend down today as the ridge to the north is shifted to the east with a front approaching from the northwest. Winds are also expected to turn to the southeast tonight as the front edges closer to the region.
The cold front is expected to enter the northwest coastal waters by Tuesday night and proceed down the island chain through Wednesday night. Ahead of the front, expect southerly winds, with stronger northwest winds behind the front. The front is also expected to bring showers, some of which may be heavy, and may be accompanied by a few thunderstorms. Northerly winds are expected to spread across the coastal waters on Thursday, with northeasterly winds returning on Friday.
A series of small, northerly swells are expected over the next couple of days, which will maintain surf along the north facing shores. A much larger northwest swell will likely produce very large to extra large surf along north and west-facing shores of the smaller islands toward the end of this week, potentially affecting west facing shores of the Big Island as well. Early energy from this swell will likely arrive on Kauai Tuesday afternoon, and then steadily build, peaking late Thursday into Friday. This swell will also bring SCA level seas to the coastal waters, as early as Wednesday morning, and spread to most waters by Thursday morning. Many waters will continue to experience SCA level seas into the weekend.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov