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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 051926
Area Forecast Discussion
National Weather Service Honolulu HI
926 AM HST Tue Jul 5 2022
Locally strong trades will continue with wetter than normal
conditions through tonight, particularly for the windward slopes
of Maui County and Oahu. Trades and shower coverage then trend
downward during the latter half of the week.
No changes to the forecast this morning, and not expecting any
significant changes with the afternoon package.
High pressure to the north of the islands continues to drive
locally strong trades to the region. A frontal remnant band caught
in the trades continues to bring wet weather to the central
islands. As of 9am, the band is focused over Oahu, with some
improvement over the islands of Maui County. However additional
clouds upstream of Maui County may bring an uptick in shower
activity later today and tonight.
Drier conditions are expected to continue over Kauai and the Big
Island, with the showers there focused over the typical windward
areas in the trade wind flow. The morning soundings out of Hilo
and Lihue confirmed the arrival of the band of mid-level dry air
centered around 700mb. This will ensure continued stability and
will limit rainfall amounts away from the most favored locales
even as shower coverage remains high. The diurnal heating will
bring some improvement by this afternoon, causing showers to trend
downward until this evening. Showers then increase in coverage
over roughly the same areas again tonight.
The high pressure to the north is expected to weaken some during
the middle of the week, which will result in a bit of a downward
trend in the trades. An upper level trough axis to the northwest
of the islands will linger through the week. This is helping to
bring some upper level clouds to the region which will also linger
through the week. These clouds are expected to be mostly
transparent, but batches of these clouds will at times be
sufficient to take the edge off of daytime heat. Locally breezy
trades will deliver periods of trade wind showers to windward
zones for the remainder of the week, but continued stability will
help limit rainfall amounts.
An area of high pressure north of the state will allow for breezy
to locally windy trades to persist through the forecast period.
This pattern will bring numerous showers to the windward sides of
the islands, along with periods of MVFR ceilings and visibility.
In addition, isolated showers may pass over the higher terrain
and onto leeward areas.
AIRMET Sierra remains in effect for mountain obscuration over
windward areas of Maui County and Oahu.
AIRMET Tango remains in effect for low-level mechanical
turbulence leeward of mountains due to strong trades.
Strong surface high pressure will remain located generally
northwest to north of the state this week and then build east this
weekend. A cold front moving down the eastern flank of this high
will briefly weaken the pressure gradient back toward the islands.
This will create a period of relatively lighter trade winds
Thursday and Friday. The front will wash out this weekend and allow
the pressure gradient to re-tighten across the waters upstream of
the state. The result will be the return of fresh to strong
trades by early next week. A Small Craft Advisory (SCA) is in
effect for the windier zones around Maui and Big Island through
Friday with the Kaiwi Channel remaining in the SCA through
No significant swells are expected the next several days. Strong
trades will support rough and choppy surf along east facing shores
through Wednesday. Late week east surf and seas will somewhat ease
going into Thursday in response to weakening upstream trades. Deep
low pressure passing southeast of New Zealand today will send
longer period southwest to south swells our direction. This swell
should produce near to above average south facing shore surf early
next week. A small, medium period east swell generated by Hurricane
Bonnie in the eastern Pacific may arrive early next week.
Small Craft Advisory until 6 PM HST Friday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Small Craft Advisory until 6 AM HST Wednesday for Kaiwi Channel.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office