Mostly quiet weather will continue through Friday, with increasing clouds and a few light showers as moisture is drawn northward on light to moderate southwesterly flow. A cold front and upper level disturbance late Friday into the weekend will bring a wetter, more unsettled pattern with heavy rain and a few thunderstorms possible, followed by strengthening trade winds early next week and then gradually improving conditions.
Overall, the weather remains fairly benign in the near term. Visible satellite imagery this afternoon shows a persistent stream of cumulus clouds feeding into Oahu as the light to moderate south-southwesterly flow pulls moisture northeastward across the area. This pattern is expected to continue into Friday, with model guidance suggesting that the moisture plume will slowly broaden across the central islands as weak surface convergence develops within the southwesterly flow. The result will be increasing cloud cover and a few passing light showers, especially where convergence is able to focus.
Attention then turns to the next cold front, which is expected to reach Kauai Friday afternoon or evening before slowing as it attempts to move down the island chain over the weekend. This front, combined with the moisture already in place, additional convergence ahead of it, and increasing instability associated with an upper-level trough and much cooler temperatures aloft, sets the stage for a wetter and more unsettled period from this weekend into early next week. Periods of heavier showers and a few thunderstorms will be possible, with a localized flooding threat developing where showers persist the longest. Behind the front, winds are expected to veer from northeasterly to easterly fairly quickly, shifting the focus for showers—and any thunderstorm activity—toward windward and mauka areas. These locations currently appear most susceptible to heavier rainfall and potential flooding, though there remains enough model spread to keep some uncertainty regarding which islands will be most impacted. That picture should sharpen as we get closer and higher- resolution guidance comes into play. In addition, cooler air aloft and ample moisture will also bring the potential for wintery precipitation to the summits of the Big Island Saturday night through Monday night.
As high pressure builds in from the north behind the front, the pressure gradient will tighten and trade winds are expected to strengthen late Sunday into Monday. Wind Advisory conditions appear likely, with the possibility of High Wind Warning-level gusts possible, particularly over and downslope of terrain, through valleys, and other local acceleration areas. While wet trade wind weather will continue during this time, the overall flooding risk should gradually decrease Tuesday onward as the bulk of the moisture advects west of the island chain on the strong trades. Trade winds are then expected to ease back to breezy levels by midweek and persist through the latter part of next week.
Weakly convergent and light SW flow is focusing a band of low clouds and scattered showers over Oahu this afternoon. Pockets of MVFR are observed with this activity, particularly in heavier showers. This line of showers will slowly advance east as additional moisture lifts toward Leeward Maui County late tonight into early Friday bringing additional showers and pockets of MVFR. By mid-afternoon Friday, a frontal rain band and accompanying breezy northerlies will be on Kauai's doorstep. AIRMET Sierra may be needed for north facing slopes of Kauai at that time.
No AIRMETs in effect.
A surface ridge over the islands will maintain gentle to moderate south to southwest winds into Friday as a front approaches. The front will move across Kauai waters Friday afternoon and evening and advance southeastward into the central islands Friday night and Saturday. The front will stall and gradually dissipate near Maui County over the weekend, leading to heavy showers and thunderstorms statewide. Strong high pressure building north of the state will drive fresh to possibly strong trade winds north of the front late Friday and Saturday. A Small Craft Advisory (SCA) may be needed for winds around Kauai and Oahu, while a building northwest swell produces seas above the 10 foot SCA threshold over most waters. Surface high pressure will expand significantly on Sunday and Monday as surface troughing develops southwest of the islands. As a result, trade winds will strengthen to near gale to gale force over many areas, with at least SCA conditions developing over all waters for winds and seas late Sunday. A slow decrease in trade winds is expected Tuesday and Wednesday, but large seas will persist.
The current northwest swell is declining, but the last in a series of large swells will arrive on Friday. Surf along exposed north and west shores will be just below High Surf Advisory thresholds into Friday morning as the current swell slowly drops and shifts out of the north-northwest. The new northwest swell (310-320 degrees) will build down the island chain on Friday. Surf along north and west shores of Kauai and Oahu will likely rise above High Surf Advisory levels during the day, and surf along exposed north and west facing shores of most islands may exceed High Surf Warning levels as the new swell peaks Friday night and early Saturday. The swell will decline sharply Saturday night, with surf expected to fall below advisory levels by Sunday morning. Small to moderate northwest swell will prevail through the remainder of the week.
Surf along east facing shores will remain very small through Friday night. Surf is expected to rapidly build and become more rough this weekend, likely exceeding the advisory level Sunday night or Monday and potentially reaching warning level Tuesday or Wednesday. Surf along south facing shores will remain small throughout the week.
None.
