textproduct: Honolulu

SYNOPSIS

Breezy east-southeast winds will persist through the weekend as a cold front stalls northwest of the state and high pressure remains anchored to the northeast. This pattern will favor showers along southeast- and east-facing slopes of the Big Island and Maui, with sea breezes and downstream convergence bringing clouds and a few showers to leeward and interior areas. Strengthening southerly flow may draw deep tropical moisture over the islands next week, bringing an increasing chance for a wetter and more unsettled pattern.

DISCUSSION

Breezy trades veered to an east-southeast direction earlier today, a bit sooner than previously anticipated. Low-level flow is expected to remain east-southeast through the weekend as a cold front approaches and stalls northwest of the state, interacting with the strong surface high pressure system anchored to the northeast. In this pattern, showers will favor southeast- and east-facing slopes of the Big Island and Maui, along with leeward and interior areas statewide as sea breezes develop within the lighter, somewhat blocked flow. Model guidance remains in good agreement through this period, keeping the front stalled just west of the islands while its parent low lifts farther northwest.

Looking ahead to next week, global models show a mid- to upper- level low rounding the base of a trough northwest of the state and spawning a surface low to the west-northwest. Strengthening southerly flow between this low and high pressure to our northeast is expected to draw deep tropical moisture (precipitable water values of 1.6 to 1.8 inches) over portions of, or possibly the entire, state beginning early to midweek. This moist southerly flow may persist through much of next week and, combined with instability associated with nearby upper-level disturbances, could support a wetter and more unsettled pattern with the potential for heavy rain and thunderstorms lasting into next weekend.

Model agreement has improved somewhat regarding the overall pattern evolution next week, and forecast confidence is gradually increasing. However, important details, including the exact placement of the deepest moisture and the strength of the southerly winds, are still coming into focus.

AVIATION

Moderately breezy easterly trades are expected to continue tonight, then turn a little more southeasterly tomorrow. Isolated to scattered showers will occur mainly windward and mauka, with MVFR possible. Expect the usual uptick in coverage and intensity of showers overnight. Still, most sites will have VFR.

AIRMET Tango remains in effect for turbulence below 8 kft along leeward sites of the islands due to the ongoing trade pattern. This is expected to remain in effect through the period.

MARINE

Trade winds have started to veer towards the east-southeast today due to the high shifting further east. Fresh to strong east to east-southeast winds will continue to persist through Thursday then slightly ease Thursday night into Friday as a front passes to our north. Fresh to strong east-southeast winds will return over the weekend. A Small Craft Advisory (SCA) remains in effect for most of the waters around the Big Island and Maui through Thursday, where winds will be strongest. In the extended, long range models are showing a large low pressure system approaching from the west early next week, which will cause the winds to veer towards the southerly direction next week. Strong southerly winds will be possible depending on how close the low pressure system gets to the islands.

The current small northwest swell will continue to decline through Thursday. A series of small west-northwest to northwest swells will maintain below average surf through at least the first half of next week. The median H1/10 for the month of March is 12 feet (Goddard-Caldwell Database). The first small west-northwest swell will arrive Thursday night and peak Friday night, followed by another small northwest bump Saturday night into Sunday. This should maintain some small surf along north and west facing through early next week. A compact storm-force low currently just off the coast of Japan could produce another small west-northwest swell around Tuesday of next week.

Choppy east shore surf did increase to seasonal averages today due to the strengthening east to east-southeast winds. Little change is expected along east facing shores over the next few days followed by a slight increase over the weekend. Surf along east facing shores should decline early next week as winds veer towards the southerly direction. Surf along south facing shores will remain small through the weekend, and some islands may see an increase in choppy surf if strong southerly winds develop early next week. A small long- period south swell is also possible around Tuesday of next week.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Thursday for Maui County Windward Waters-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.