HIC 728   9.15.20 ONLINE+INSTORE

Big Picture

Monday the 21st– Sunday September 27th 

Local Weather Outlook –

More nice and warm summer to fall days with stable Trades.

By mid-week, a more well-developed high pressure cell sets up north of us ushering in a period of moderate to isolated fresh ENE trades for Wednesday through Friday. Then Trades may ease over the weekend again.

The likelihood that any tropical cyclones will influence Hawaii during the period remains very low but we do plan on getting some small East swell (below).  Rain also will be limited to that from passing windward/Mauka trade wind showers.  It has been a long, hot and particularly dry summer, with much of the State now in some form of abnormally dry or drought conditions.

Surf Outlook –

North and West Shores:   First solid North swell of the season forecast for late Wednesday into Saturday. 

Surf remains tiny to small (Monday still had fun shoulder high NNW-NNE). Then, Wednesday afternoon some fun NNW builds to near 4′ sets. It will peak from the North at 5-7′ Thursday. The source kicked in last Friday with a system developing off the southern tip of Kamchatka.  It was forecasted to deepen over the weekend over the Aleutians with 40-45mph sustained winds. Models showed the low strengthening further and broadening on the 20th, followed by development of a long, wide fetch of 40mph winds on the 21st  and 22nd.  Although a good portion of the swell reaching the islands from this system will be due to angular spreading, the width of the fetch and the length of time that it persisted will make for a moderate and long-lived event locally.  Surf should rise to heights of 4-7’ by Thursday through out the morning.  Surf will fade Friday to 3-6′ out of the north.  Saturday should keep dropping in the 2-4’+ range before. Sunday see’s progressively smaller and more NNE direction.

Despite its northerly orientation, this week’s swell should manifest itself at Westside northerly focal reefs at 2-4′ maybe + on the peak periods Thursday, with less wrap Friday and and far less on Saturday. The North will combo with a new SSW. See below.

South Shore:  Best run of south shore surf in quite a while, with plenty of consistency…

Last weekend had Surf increase from a cyclone that occurred south of Tasmania around the 10th.  This system had 55+mph sustained winds, approaching the South Island of New Zealand on the 11th.  Surf from this system rose over Friday night, becoming 2-3’ very isolated and occ. 4’ over the weekend.  The system was followed up by a larger fetch of 40-50mph winds south of Australia on the 12th, which moved under Tasmania on the 13th.  Long period swell (20+ sec) from this system filled in underneath the previously mentioned swell on Sunday and became the dominant swell by Monday with heights of 2-3′ average.  Tuesday should still be around 2-3’.  Due to the breadth and longevity of the associated fetch, this swell will linger well into mid-week.

Another similar fetch pushed underneath Australia and Tasmania from the 15th to the 17th, although winds were a notch slower.  Long period forerunners from this fetch will arrive locally on Thursday the 24th and rise throughout the day on Friday.  Saturday peaks at slightly below the previous event, with surf heights at 2-3’+.  A redevelopment of this fetch occured Friday-Sat southeast of New Zealand.  This redevelopment will likely lead to another round of long period swell beginning overnight on Saturday the 26th and rising on Sunday.

There’s even more solid SSW swell in the early October…fingers crossed.

East Shores:  Starts off small 2′ average, but trades and northerly swell kick in esp. Thursday…

Winds were quite light (<10mph) along our typical trade wind fetch last week, hence trade wind swell is currently tiny with short periods.  Most of the waves reaching east shore breaks have been  from the previously mentioned northeasterly sources.  The situation should remain similar until the new N and trade swell ramp up Wednesday nite into Thursday.

Thursday, eastside breaks which receive solid north swell, becoming 2-4’ with isolated higher towards Kahuku and for N focal reefs.  Later Friday and over the weekend the north to NNE swell gradually drops, falling to 1-3’ by Sunday.  Spots oriented toward the east will see typical 1-2’ trade swell between Thursday and into early next work week.



The West Pac Tropics: None for the upcoming week.

Long-range views are seldom 20/20. Prep for some adjustments.



Surf Climatology HERE

NWS criteria for High Surf Advisories (first number) & Warnings (second number).

All surf height observations & forecasts are for full ‘face’ surf height, or ‘trough to the crest’ of the wave.

North-Facing Shores 15 Feet and 25 Feet

West-Facing Shores – Remaining Islands 12 Feet and 20 Feet

West-Facing Shores – Big Island 8 Feet and 12 Feet

South-Facing Shores -(Advisory) 8 Feet and (warning) 15 Feet

East-Facing Shores – 8 Feet and 15 Feet

Get the latest Central Pac Hawaii HERE

For the SNN Buoys ‘per shore’ displayed   HERE

Note: Spectral density graph in the SNN Buoy Page HERE can show ‘slivers’ of forerunners that initial text readings of new swells which often do not ‘show’ till later on written/text buoy updates. Also, note the vertical graph is not ‘wave height’ rather its a measure of wave energy in hertz (frequency or cycles/sec) for the whole ‘band’ (the distribution of power/period in the total wave energy field/spectrum).

Links: Get the latest on the Eastern North Pac GO HERE 

For more on the West Pac Typhoons GO HERE

Common Terms:  Split Jetstream

Blocking ridge

Short-wave tough

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