textproduct: Honolulu

SYNOPSIS

A strong, dominating surface high builds north of the Hawaiian Islands resulting in trades making a return through much of next week. Trades will strengthen into moderate to breezy conditions Monday and Tuesday, easing thereafter as the aforementioned surface high begins to shift eastward and weaken. Drier trades continue through the remainder of the week ahead of a possible frontal boundary toward the end of the outlook period.

DISCUSSION

A strong, dominating surface high continues to build in the central Pacific leading to the local pressure gradient tightening. This will allow trades to return to the forecast and overrun the stationary front just north of the islands. As the front dissipates, it will also open the door for any remnant moisture associated with it to advance southward toward the islands, and may bring additional showers to the western islands through the early portion of next week, namely Monday and Tuesday. In fact, model total precipitable water (PWAT) normalized anomalies portray a positive, wetter than average moisture content across the islands during this time. Otherwise, trade showers and clouds will focus predominately across windward and mauka areas.

Latest model guidance suggests that the aforementioned surface high will begin to shift eastward and weaken by midweek, weakening the local pressure gradient, allowing trades to ease and veer more southeasterly. Drier trades are expected Wednesday as a more stable airmass propagates across the islands, persisting through the reminder of the week.

Additionally, model guidance remains in reasonable agreement, proposing another frontal boundary just west of the islands toward the end of the outlook period. Further analysis will be necessary to determine the timing and impacts of this front, as confidence remains too low for now.

AVIATION

Clouds and isolated showers linger across the state, bringing occasional MVFR conditions, namely to Kauai and leeward and interior aspects of the Big Island. Light winds will continue through the morning, but will gradually strengthen this afternoon as the trade winds return. Showers embedded within the trade winds may bring brief MVFR conditions to windward and mauka areas.

AIRMET Sierra for mountain obscuration is in effect for Kauai as lingering showers and clouds persist.

MARINE

The high pressure ridge will finally build back into the islands from the north today. Expect a return to strengthening easterly trade winds over the next few days. Clouds and showers will diminish as this stable ridge builds in over the Hawaii region. Increasing trade winds through the day has triggered the issuance of a Small Craft Advisory this morning for the typical windier waters and channels around Maui and the Big Island lasting at least into Tuesday.

The current overlapping moderate, medium period north (345-010 degrees) swells will gradually decline through Tuesday. A similarly sized north-northeast swell is expected to arrive late Wednesday and persist through Friday, with the largest swells favoring the eastern end of the island chain. Periods of additional smaller northwest (310 to 330 degree) swell energy will overlap this larger northerly swell, increasing surf heights at shores exposed to northwest swell directions. A Marine Weather Statement for north swell generated harbor surges, along north facing harbors including Kahului and Hilo, remains in effect through this afternoon.

For east facing shores, wrapping north swell will produce moderate surf along exposed coastlines today, while sheltered areas will experience smaller surf. Returning trade winds will produce building surf on Monday, with rough conditions above seasonal averages possible from Monday night into Wednesday. As trade winds over and upwind of the islands ease during the second half of the week. Surf along south facing shores will remain very small with fleeting background south and southwest swell energy through the week.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.