Synopsis18 Jun 2019 02:01:00 GMT: Moderate east-southeast winds will return to a more typical easterly direction late Tuesday. Showers will continue to be focused across windward slopes, though we will likely see increased clouds and a few showers Tuesday afternoon. Winds will decrease again and shift out of the southeast across most islands on Friday and the weekend.
Discussion18 Jun 2019 02:01:00 GMT: Easterly trade winds have veered out of the east-southeast from Maui to Kauai, leading to widespread leeward sea breezes this afternoon. This wind shift occurred as a longwave trough, which has been present for the last couple of weeks, deepened several hundred miles northwest of the state. This invigorated a surface trough near Midway Atoll and caused the trade-wind-generating surface high to drift far northeast of the state. Expect the east- southeasterly winds to hold from Kauai to Maui into Tuesday afternoon, while easterly trades hold on the Big Island.
Modest showers will continue to favor windward slopes, though afternoon leeward sea breezes will likely trigger a few showers over leeward areas during the afternoon hours through Tuesday. These sea breezes have produced spotty showers over interior Oahu today, but aside from a brief shower on the upper slopes of Mauna Loa, leeward areas elsewhere have been dry. A pocket of slightly enhanced moisture is riding just off the windward coasts of Maui to Kauai this afternoon, giving these islands the highest potential for windward showers tonight. As the pocket of moisture advances westward tomorrow, the greatest chances for showers, both windward and leeward, will be on Kauai. Though weakened a bit by an upper-level trough, mid-level ridging should keep the atmosphere stable and inhibit heavy shower development.
As the trough to the northwest of Kauai weakens, trades will shift back to a more typical, easterly direction late Tuesday, and modest rainfall will be confined to windward slopes as a stable and somewhat dry air mass fills in from the east.
Trades are expected to weaken and shift southeasterly over portions of the island chain on Friday and persist through much of the weekend. For now, the GFS and ECMWF are maintaining somewhat dry and stable conditions over the state, so we are not expecting any significant rainfall.
Aviation18 Jun 2019 02:01:00 GMT: Moderate to fresh winds out of the east-southeast will back towards the east by this evening. Sea breezes set in over some of the leeward sections today bringing cloud build ups and showers over these areas. Brief mountain obscurations are expected over the next couple of hours for leeward areas. These showers will decrease around sunset, improving ceilings and visibility for the leeward sides. Windward areas will see low clouds and a few incoming showers through the night. No AIRMETs are in effect at this time, however, the potential for clouds to fill in over windward slopes will increase late tonight and early Tuesday morning which could prompt an AIRMET for tempo mountain obscuration. Winds will also strengthen slightly on Tuesday increasing the likelihood for moderate leeward turbulence.
Marine18 Jun 2019 02:01:00 GMT: The combination of a trough to our west and high pressure far northeast of the state will lead to fresh to locally strong east to east-southeast winds across area waters during the next couple of days. Due to the southeasterly component, locally strong winds are expected for parts of the windward zones of the Big Island and Maui through tonight. A Small Craft Advisory (SCA) is in effect for the Alenuihaha Channel, south of Big Island and the windward zones of Big Island and Maui. Winds may shift slightly more easterly on Tuesday, which may cause locally strong winds across the Pailolo Channel and may allow the winds to decrease over the windward zones of Maui and the Big Island. We will continue to monitor the situation and update the SCA if necessary. As the trough to our west strengthens Thursday into the weekend, winds are expected to gradually weaken and veer southeast by late Friday or Saturday.
The current south-southwest swell will continue to decline through the first half of the week. We should see a slight bump Tuesday into Wednesday as a new small long-period south-southwest swell fills in. So far thou, no signs of the new long-period swell on the buoys as of this afternoon. Minimal surf is expected towards the latter half of the week with only background south swells expected.
A small tiny pulse of northwest swell will be possible on Tuesday. Besides that, only background energy out of the northwest is expected through rest of the week. Surf along east facing shores will begin to rise this week as trade winds become more established, especially for the east and central isles. A short-period northeast swell is possible over the weekend due to a fetch of strong northeast winds expected to develop west of the California coast during the middle of the week.
HFO Watches/Warnings/Advisories18 Jun 2019 02:01:00 GMT: Small Craft Advisory until 6 PM HST Wednesday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 AM HST Tuesday for Maui County Windward Waters, Big Island Windward Waters.
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