Photo Credit: Braden Jarvis

West Kaua’i

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 86 to 91 near the shore to around 76 above 3000 feet. Southeast winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 40 percent.

Tonight: Mostly clear. Lows around 71 near the shore to around 61 above 3000 feet. Light winds.

Wednesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 86 to 91 near the shore to around 77 above 3000 feet. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny with isolated showers. Highs 84 to 91. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 72. Northeast winds around 10 mph.

Wednesday: Mostly sunny. Highs 84 to 92. Northeast winds around 10 mph.

Kaua’i Mountains

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 83 in the valleys to around 68 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 64 to 70 in the valleys to around 59 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 85 in the valleys to around 67 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 78 to 88. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 65 to 74. East winds up to 10 mph.

Wednesday: Mostly sunny. Isolated showers in the afternoon. Highs 78 to 87. East winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 77 to 88. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 64 to 76. Northeast winds around 10 mph.

Wednesday: Mostly sunny. Isolated showers in the afternoon. Highs 77 to 88. Northeast winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The relatively weak trade winds in the vicinity of the islands will allow the development of alternating afternoon sea breezes and nighttime land breezes into Wednesday. This weather pattern favors the development of clouds and spotty showers over leeward and interior sections each afternoon, followed by clearing skies overnight. A weak front pushing into the western end of the island chain mid-week is expected to usher in a brief period of light to moderate trade winds from Thursday into Friday. By this weekend, weakening background winds will likely result in a return of the land and sea breeze weather pattern.

Discussion

The western end of a weak surface ridge appears to be slightly more than 200 miles north of Lihue early this morning. Elsewhere, the leading edge of a nearly 120 mile wide band of overcast clouds and showers associated with a cold front is located about 440 miles northwest of Lihue. This leading edge has been moving toward the southeast at about 10 mph during the past several hours. This approaching front will continue to erode the ridge north of the area, so the trade winds will remain relatively weak across the state during the next 24 to 30 hours. The weak background flow allowed local land breezes to become established over each of the islands overnight. Loops of satellite imagery and radar reflectivity show patches of low clouds and isolated showers near the leeward coastline of the Big Island and in the vicinity of windward Oahu. Elsewhere, the downslope winds have resulted in mostly clear skies across the remainder of the land areas.
The forecast guidance indicates the relatively weak background flow will likely persist through early Wednesday as the front pushes down toward the region. Expect local sea breezes to develop from late this morning through the afternoon, with variable amounts of clouds and some brief showers forming over some leeward and interior sections later today. Clearing skies are expected over most areas tonight. The front will be weakening as it arrives Wednesday, so afternoon sea breezes may still form over many islands. The pressure gradient will begin to tighten starting late Wednesday, especially over the western islands. This will likely allow light to moderate trade winds to spread over parts of the state from Wednesday night through Thursday and Friday.
Note that the arrival of the weakening front may increase low cloud cover and showers over portions of Kauai. Some of these clouds and showers may also reach Oahu, and possibly Molokai and Lanai. However, the front will likely dissipate before it reaches Maui and the Big Island.
The weather pattern will likely change again this weekend as another front pushes down toward the region from the northwest. The model guidance depicts light southeast to south winds ahead of this front. This will result in a return of afternoon sea breezes and nighttime land breezes from Saturday into Sunday. The general southerly background flow may bring an uptick in showers over some south and southeast facing slopes, especially on Sunday.
Looking ahead to early next week, the forecast model output continues to depict a broad low pressure system moving down to a position far north-northwest of the state. The actual track and intensity of this area of low pressure, which is related to the front moving toward the region this weekend, remains somewhat uncertain at this time. Therefore, we will monitor future model runs to determine if the broad circulation around this low may be capable of transporting enhanced moisture from the tropics into the islands from next Monday into Tuesday. For now, we have partly to mostly cloudy skies with increasing shower coverage in the forecast next Monday through Tuesday, especially over the western islands.

Aviation

Light trades will persist through today and tonight, with VFR conditions generally prevailing. In this weaker flow pattern, land and sea breeze development can be expected. For the rest of the night into the morning hours, any moisture in the light trades will help to keep some clouds and isolated showers across the windward areas, while land breezes will help to limit cloud cover across leeward areas. During the day today, leeward and interior portions can expect an increase in clouds and some spotty showers with local sea breezes in the afternoon.
There are currently no AIRMETS in effect and none are anticipated today or tonight.

Marine

The current northwest swell is on the rise, and is expected to rapidly build through the day with the north and west facing shores of the smaller islands seeing warning level surf. Expect surf to build along north and west facing shores of the smaller islands today, peaking tonight and Wednesday. Although the Big Island will be blocked from most of this swell, there is enough of a westerly component for surf to rise along the west facing shores of the Big Island to approach advisory levels. As a result, a High Surf Advisory has been posted for the west facing shores of the Big Island for today through tomorrow.
This swell will also build seas to Small Craft Advisory (SCA) levels across much of the coastal waters today through Wednesday night. A SCA remains posted for the coastal waters around Kauai and Oahu, and the waters north of Maui County starting at 6 am today. The SCA may need to be expanded to additional waters later today as the swell spreads across the coastal waters.
In addition to the northwest swell, a series of south-southwest swells will keep surf along south facing shores well above the October average through much of the work week. The current south- southwest swell will be reinforced by a slightly larger south- southwest swell Wednesday into Thursday. East shore surf will generally remain small during the next 7 days, but in areas exposed to wrap from the northwest or the south should see larger surf.
Trade winds will remain in the light to moderate range into the middle of the week as a front passes north of the state. The tail end of a weakening front could push southward into the western islands Thursday and Friday, with a new high building in behind the front. This could strengthen the trades back to moderate and fresh levels over the western end of the state, with lighter trades prevailing over the eastern end. However, the increase in winds is looking to be short-lived, as the trades appear to ease again this weekend as a new from approaches from the northwest.

HFO Watches/Warnings/Advisories

High Surf Warning from 6 AM this morning to 6 PM HST Wednesday for north and west facing shores of Kauai, Niihau, Oahu, and Molokai, and for north facing shores of Maui.
High Surf Advisory from 6 AM this morning to 6 PM HST Wednesday for west facing shores of the Big Island.
Small Craft Advisory from 6 AM this morning to 6 PM 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.

Data Courtesy of NOAA.gov