Big Picture

BIG Picture updated 330pm, Sunday, April 20

Monday, April 21^st – Tuesday, April 29^th

Trades shifting to Kona and light and variable winds for most of the week.

An extensive ridge of high pressure stretches from Honshu to the North American west coast. Locally, ENE trades have briefly returned at moderate paces (10-20mph), though not strong enough to overcome afternoon sea breezes over the leeward coast. Early in the week, a trough to the NW of Hawaii will shift SE and deepen into a closed area of low pressure. The trade wind should shift East and weaken to light to moderate paces (5-15mph) on Monday. The wind should shift S-SSE at light paces (5-10mph) on Tuesday and increase to light to moderate paces on Wednesday as the low deepens. For Thursday and Friday, the flow should turn SE, which should manifest as light and variable conditions on Oahu under the shadow of the Big Island. Light and variable conditions appear probable for the weekend. Trades should gradually return early next week as the system lifts to the NE and out of the area. Unsettled weather, especially on Tuesday and Wednesday, should persist through most of the period. Drier weather could finally return early next week.

Surf Outlook –

North Shore and West Shores: Slow for most of this week with an uptick towards Saturday…

Recent/Now: Surf on Sunday was 2-3’ Hawaiian scale on a dropping 12 second period NNW swell. This is towards the tail end of a moderate to large NW-NNW swell that peaked at 5-7’ on Friday. The source was a large cyclone that approached the eastern Aleutian Islands Apr 15-16. Surf from this source should drop to 1-2’ on Monday.

Next: A large system emerged into the western North Pacific from Hokkaido Apr 15-16. It aimed a wide but short area of 35-45mph winds at Hawaii. The system slowly weakened as it tracked eastward Apr 17. Moderate period forerunners of 15 seconds from the NW should arrive overnight Sunday. This energy began to ping the NW buoys on Sunday. Surf should slowly rise to 1-2’ by midday Monday and hold into early Wednesday. Heights should drop late Wednesday to below 2’ on Thursday and Friday.

Finally: Models form an area of low pressure east of northern Honshu late Apr 20. The system is predicted to deepen to a large, storm force system as it travels parallel to the Kuril Islands Apr 21-22. Long period forerunners of 17-18 seconds from the NW should arrive overnight Friday. Surf should rise to 2-3’ early Saturday and 2-3’+ in the afternoon. It should peak at dawn Sunday at 2-4’ and drop to 1-2’+ early Monday and 1-2’ early Tuesday.

Outlook: Though storm activity is gradually trending down, long range model output depicts a series of systems racing across the North Pacific Apr 27 to the first week of May. This suggests most days to be at or near 2’ with peak days of around 3’ during the first week of May.

South Shores: Surf going above the summer average early this week…

Recent/Now/Next (ABOVE AVERAGE): Surf on Sunday was 1-2’ very occ. 3’ on a mix of a 15 second period SSW swell and a 20 second period SSW-S swell. The source of the former was a shortwave trough that passed south of New Zealand Apr 11-12 with 35-45mph winds aimed to the ENE. The latter was from a compact storm with 55-70mph winds. This system moved fairly quickly to the east but probably generated a small area of seas to near 40’. Then right behind it was a longwave trough that directed a long fetch of 35-45mph winds to the NE from SE of New Zealand Apr 14-15, which built on existing seas and will make for a prolonged event. Surf should drop to 1-occ. 2’ from the SSW but rise to 1-2’ occ. + from the SSW-South on Monday. It should peak Tuesday at 2-3’ occ. + and hold into early Wednesday. There could be 4’ sets at the focal reefs. Surf should drop to 1-2’ occ. 3’ early Thursday, 1-2’ occ. + early Friday, and 1-occ. 2’ early Saturday.

Next: Increasing Kona winds should bring very short period energy in the 5-6 second period band from the S-SSE Wednesday, peaking on Thursday at 1-2’ and dropping on Friday. This should make for choppy conditions.

Next: During mid-April, Tropical Cyclone Tam tracked southward and parallel to the islands of Vanuatu. It then merged with and provided fuel to a large subtropical storm over the north Tasman Sea. Most of the winds from the subtropical cyclone were aimed away from Hawaii but it became more favorable Apr 18-19 with a small area of 35-50mph winds aimed to the NE. 15-16 second period forerunners from the SW could arrive Friday. Surf should rise to 1-occ. 2’ for Saturday and Sunday. It should drop to 1-1.5’ on Monday.

Finally: An exceptionally wide trough traveled along the coast of Antarctica Apr 18-19. The very wide fetch of 40-50mph winds gained slightly better aim to the NE as it approached the central South Pacific Apr 19-20. It could bring low, long period energy from the South on Saturday with surf rising to 1-occ. 2’ late in the day and into Sunday. Surf should drop to 1-1.5’ early next week.

Outlook: More substantial troughing will replace a massive ridge of high pressure east of New Zealand beginning on Apr 22. This will increase surf potential in the long term. The first trough is modelled to setup SE of New Zealand with a long, wide fetch of 30-40mph winds aimed to the NE Apr 22-23. This will be followed quickly by a strong trough Apr 23-24. It should be sufficient to bring an extended period of surf to near the summer average from the SSW Apr 30 to May 2. However, the very long range still shows nothing exceptional for the islands heading towards the middle of May.

East Shores: Surf dropping early this week, hitting a minimum early next week…

Recent/Now/Next/Finally: Surf on Sunday was 1-3’ on primarily ENE-NE trade wind swell with small North wrap mixing in. This will not last long as Kona winds replace the trade winds. This should cause surf from the wind swell to drop to 1-2’+ on Monday and 2’ or smaller for the remainder of the week. While the local winds will be light, the trade winds at 600-900 nautical miles upstream of the islands should be strong enough to maintain tiny, distant wind swell. Surf should reach a minimum early next week (near flat) as a trough pushes the distant trades further away.

Outlook: Models agree that trade wind swell should rebound to 2’+ towards the start of May as a new ridge of high pressure builds in from the west and brings back moderate to fresh E-ENE trades.

Forecaster Jonathan Huynh

NEW 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) 10 Feet (up 2′) and (warning) 15 Feet

East-Facing Shores – 10 Feet (up 2′) 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).