Photo Credit: Jeni Ji Cousins

West Side

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 81 to 89. Northeast winds around 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers after midnight. Lows 69 to 76. Northeast winds around 10 mph. Chance of rain 20 percent.

Thursday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs 81 to 89. Northeast winds around 10 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

South Side

Today: Sunny in the morning then becoming partly sunny. Highs around 88. Northeast winds around 10 mph.

Tonight: Mostly clear. Lows 66 to 75. Northeast winds around 10 mph.

Thursday: Sunny in the morning then becoming partly sunny. Highs around 88. Northeast winds around 10 mph.

North Shore

Today: Mostly sunny with isolated showers. Highs 78 to 87 near the shore to around 68 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 74 near the shore to 48 to 54 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 86 near the shore to around 68 near 5000 feet. Northeast winds around 10 mph. Chance of rain 40 percent.

Central Maui

Today: Sunny. Highs 83 to 90. East winds around 10 mph.

Tonight: Mostly clear. Isolated showers after midnight. Lows 66 to 72. Northeast winds around 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Highs 82 to 89. Northeast winds around 10 mph.

Upcountry

Today: Sunny. Highs around 64 at the visitor center to around 59 at the summit. East winds around 10 mph.

Tonight: Mostly clear. Lows around 48 at the visitor center to around 45 at the summit. Northeast winds 10 to 15 mph.

Thursday: Sunny and breezy. Isolated showers in the afternoon. Highs around 63 at the visitor center to around 59 at the summit. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

East Maui

Today: Mostly sunny with isolated showers. Highs 78 to 87 near the shore to around 68 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 69 to 74 near the shore to 48 to 54 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 86 near the shore to around 68 near 5000 feet. Northeast winds around 10 mph. Chance of rain 40 percent.

Lanai City

Today: Mostly sunny. Highs 73 to 81. East winds around 10 mph shifting to the south in the afternoon.

Tonight: Mostly clear. Lows around 66. Northeast winds around 10 mph.

Thursday: Mostly sunny. Isolated showers in the afternoon. Highs 73 to 81. East winds around 10 mph. Chance of rain 20 percent.

Kaunakakai

Today: Sunny in the morning then becoming partly sunny. Highs 70 to 92. East winds around 10 mph shifting to the north up to 10 mph in the afternoon.

Tonight: Partly cloudy with isolated showers. Lows 59 to 75. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs 70 to 92. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Light winds due to a weakening front approaching Kauai from the northwest will allow the development of sea breezes this afternoon. This weather pattern favors clouds and spotty showers forming over leeward and interior sections during the afternoon, The arrival of the weak front over the western end of the island chain is expected to usher in light to moderate trade winds from late tonight and Thursday into Friday. The front will also bring increasing trade showers on Kauai early Thursday, and possibly on Oahu late Thursday. By this weekend, light background winds will likely result in a return of an alternating afternoon sea breeze and nighttime land breeze weather pattern.

Discussion

The ragged leading edge of a nearly 130 mile wide band of broken to overcast low clouds and showers associated with a weakening front is located about 220 miles north-northwest of Lihue. This leading edge has been moving slowly toward the south-southeast early this morning. The close proximity of the front to the islands has relaxed the pressure gradient across the area. This has resulted in weak background flow, which allowed local land breezes to become established over each of the islands starting last evening. Loops of satellite imagery and radar reflectivity data show a few narrow bands of low clouds with embedded light isolated showers moving in from the northeast toward the windward sides of the some of the islands. Elsewhere, the downslope winds are keeping mostly clear skies above most leeward and interior sections.
The forecast model output indicates the relatively light background flow will likely persist this morning as the weak front pushes down toward the region. Expect local sea breezes to develop on most islands starting late this morning, and continuing through this afternoon. This will produce variable amounts of low clouds and some brief showers over some leeward and interior sections by this afternoon.
The pressure gradient will likely begin to tighten starting tonight, especially over the western islands. This will likely allow light to moderate trade winds to spread over parts of the state Thursday and Friday. Note that the arrival of the weak front may increase low cloud cover and trade showers over portions of Kauai late tonight and Thursday. Some of these low clouds and trade showers may also reach Oahu by late Thursday. However, the front will likely dissipate before it reaches Maui County and the Big Island. Therefore the eastern end of the state will likely remain in a rather dry land and sea breeze pattern Thursday and Friday.
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 Friday night into Sunday. The general southerly background flow may bring an uptick in showers over some south and southeast facing slopes, especially on Sunday.
The consensus of the forecast model output continues to show a low pressure system moving down to a position far north-northwest of the state early next week. The broad circulation around this low may be capable of transporting enhanced moisture from the tropics into the islands from next Monday through Tuesday. This type of weather scenario often results in high humidity and widespread cloud cover and showers, but does not always result in the development of significant deep convection. We will need to monitor the model output during the next few days to determine if significant, or widespread heavy rainfall may occur early next week. At this time, the forecast indicates the best chances for widespread and/or heavier precipitation is over the leeward / interior Big Island, where deep convection may develop during the afternoon due to daytime heating combined with the enhanced moisture and some dynamic instability. Elsewhere, expect partly to mostly cloudy skies with increasing shower coverage over the smaller islands next Monday through Tuesday.

Aviation

Light to locally moderate trades will continue today with VFR conditions generally prevailing across the Hawaiian Islands. With this relatively weak background flow, sea breezes will increase cloud cover and shower activity across interior and leeward areas during the afternoon hours again today. Then the pressure gradient will tighten this evening, strengthening trades slightly overnight. These slightly increased wind speeds may limit nighttime land breeze development to the more protected areas. In addition, an approaching weak cold front will bring more moisture to the northwestern part of the state, increasing shower activity mostly across Kauai this afternoon and tonight.
There are currently no AIRMETS in effect and none are anticipated at this time.

Marine

The first significant northwest swell of the season peaked well above the predicted levels overnight, which is resulting in Small Craft Advisory (SCA) level seas and warning level surf for exposed waters and shores. Although observations at the offshore buoys to the northwest and the nearshore PacIOOS Hanalei and Waimea buoys are beginning to slowly ease, expect the surf to hold well above warning levels for exposed north and west facing shores of the smaller islands today (highest through the morning hours). Some of this energy will make it to the west facing shores of the Big Island today, pushing surf to the advisory level.
Surf at this level coinciding with the early morning high tide cycle today (water levels are running around half of a foot higher than predicted) could lead to some significant beach erosion and overwash in the typical low-lying coastal areas and roadways for the smaller islands.
Expect the swell to slowly ease through the second half of the week as the peak direction shifts from the northwest to the north. Surf heights are forecast to dip to advisory levels by Thursday as this swell slowly eases. The SCA for seas will likely hold for some waters through Thursday before lowering below the 10 ft threshold.
Surf along south facing shores will hold above the October average through the week as overlapping south-southwest swells move through. A fresh long-period, south-southwest swell is expected to gradually fill in through the day today, then peak Thursday through Friday. Surf will ease into the weekend as this swell moves out.
Surf along east facing shores will remain small through Thursday, then pick up Friday due to a moderate northeast swell (short-period) associated with the strong gradient between the front to the north and high pressure building in behind it Wednesday through Thursday. This will be a short-lived event with a quick drop off expected by Saturday.
Trades will remain in the light to moderate range through Friday for most areas, which will allow localized overnight land breezes and afternoon sea breezes to form near the coasts. The exception will be over the Kauai and Oahu waters late Thursday through Friday as the tail-end of an old front drifts south into the area. Guidance depicts the trades reaching the fresh to locally strong range through this time, with the best chances for the strong winds being over the Kauai waters. This will be short-lived due to another front approaching from the northwest, which will lead to a return of light and variable winds by Saturday. As the front approaches from the northwest, guidance is showing the winds shifting out of the south to southwest and increasing to moderate levels through the day Sunday.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST this evening for north and west facing shores of Kauai, Niihau, Oahu, and Molokai, and for north facing shores of Maui.
High Surf Advisory until 6 PM HST this evening for west facing shores of the Big Island.
Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters.

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Data Courtesy of NOAA.gov