This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

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Susan Kieffer can be contacted at s1kieffer at gmail.com

Tuesday, January 21, 2014

50' waves for Hawaii, and crummy surfing? What's the problem?

From CNN.com here, photographer is
Kent Mishmura, Getty Images.
When the surf is just right, surfers of the world gather in Oahu for "just one day of quality surf" when wave heights reach 40' or more, the largest waves since 2004.. The National Weather service has issued an gale warning that "An extremely large northwest swell will roll through the area Tuesday through Thursday." The significant wave height is expected to reach 20 feet (significant wave height is the average height of the highest 1/3 of the waves, and individual waves can be more than twice this value.) The large northwest swell is arriving Tuesday night, producing high surf along the north and west-facing shores of the islands over Wednesday and Thursday.
     I couldn't find any specific reference to the source of the northwest swell. There are two storms listed here, Tropical Storm LINGLING, and Tropical Depression INVEST, and I'm assuming that one or both are the drivers of the swell. However, neither of these is mentioned in the 1/21/2014 NOAA description of conditions appended at the end of this post. (Note that it discusses both big waves during the past week, and forecasted for the next few days.) NOAA attributes the waves to a low with hurricane force winds far to the northwest of Hawaii.

     Countering this driver of good big waves is a fast moving cold front approaching Kauai from the northwest.  This front will cause southwesterly winds to increase over Oahu and Lihue (the two northernmost large islands in the Hawaiian chain) over the next two days (Tuesday and Wednesday), and the winds will then spread southeast down the other islands. The front will produce gusty winds and the gusty winds will destroy the "quality" (a quote from Glen Moncata, the organizer of a potential big surf competition) of the waves required for prime surfing conditions.
    Aside from cancellation of a potential big surf event, there is a geologic implication in all this: beach erosion on the North Shore may be severe. It is an ongoing problem in Hawaii, and reports are that there are a number of North Shore homes that may be imperiled by the wave action.

The NOAA statement: of 1/21/2014:

Summary: overlapping winter caliber events.
Detailed: mid Friday on northern shores has extra large breakers, meaning surf on outer reefs, from 295-320 degrees with 12-17 second periods. Heights should lower on Saturday.
A strong jet stream has been steering a series of deep surface low pressure systems across the NW to N central Pacific since 1/11. This active pattern should keep events peaking above winter average levels arriving locally with a 1-2 days spacing 1/18-25.
A complex pattern produced the extra-large surf of 1/17. There were two remote separate low pressures cells and associated fetches and a nearby fetch area of gales. The longer-period swell from the remote sources peaked Thursday afternoon into the night. The nearby gales had significant westerly component, as seen by comparing peak wave heights from the Hanalei and Waimea buoys, 19 feet and 15 feet, respectively for overnight to morning 1/17. The more westerly component is shadowed on Oahu by Kauai. The second low pressure of the remote low cells had an associated captured fetch over the 305-320 degree band that stretched from the Kuril Islands to near 30°N, 170°W, or over 2200 nm, making for a long-lived event. Jason altimeter data from 18Z 1/16 in a region about 1000 nm away gives confidence for continued elevated surf on Saturday 1/18 from 305-320 degrees, nosing down below extra-large.
The complex pattern simplified to one deep low pressure cell that occluded near 40°N, 160°W on Thursday 1/16. The center of this low tracked N to the Aleutians by early Friday 1/17. Severe gales over the 340-360 degree band, and angular spreading from seas aimed E of Hawaii should allow moderate energy from 330-010 degrees building late Saturday, peaking Sunday, and dropping Monday.
Further west, a new low pressure cell intensified near 35°N, 175°E Thursday afternoon. This hurricane-force system crossed the dateline Thursday night near 38°N, and is modelled to be north of Hawaii near 40°N by Saturday morning. With a compact size and fast track, the fetch areas are limited in length and duration for growth of seas. The GFS input to Wave Watch III, ww3, predicts the peak near dawn Sunday morning with 12 feet at 17 seconds from 320 degrees. This forecast /was' predicting higher swell for two reasons. First, the ww3 has shown a low bias for sources of gale or stronger winds with fetch heads within 1000 to 1500 nm away. Second, there was a historic low pressure cell with similar track, track speed, size, and depth of central pressure January 8-9 2004 that resulted in Waimea buoy showing a short-lived maximum above 18 feet at 20 seconds on January 10, hence, giant surf. This duration of the most elevated heights is expected to be short, about a 12 hours, centered on late Sunday morning from 300-320 degrees.
However, Sunday morning update, overnight observations from buoy 51101 northwest of Kauai indicate that swell heights are not as large as originally anticipated, and are running slightly lower than Wave Watch III guidance. Therefore, this swell forecast has been lowered, closer to Wave Watch III guidance, for Sunday.
Surf should drop to within high to extra-large on Monday from 310-330 degrees as a new event arrives.
A new surface low pressure is piggy-backing the hurricane-force system near the dateline on 1/17. The new cell is modelled to be weaker with a E track about a day behind. Gales to severe gales are modelled to set up over the 315-330 degree band, reaching to within 1000 nm of Hawaii on Sunday. Forerunners are due locally Monday afternoon, with the event peaking in the wee hours Tuesday. Heights should slowly decline into Tuesday night as a new event arrives.
Models are showing a surface low pressure deepening to hurricane force west of the dateline 1/19, tracking east across the dateline near 40°N 1/20, continuing east to near 165°W near 40°N Tuesday, then turning north into Wednesday. This should make for giant surf by the wee hours 1/22 from within 290-330 degrees. The track, track speed, size, and depth of central pressure are similar to low pressure systems that generated giant surf locally of January 28, 1998, February 23, 1986, and December 1 and 4, 1969. It is too early for specifics, other than noting that this could potentially be the type of surf episode on order of decadal turn-around. This type of surf episode is not only well above average, but long-lived, on the order of 24-36 hours, which makes for greater coastal impact. Local tides will be in the neap phase 1/22-23 which offsets wave run up potential. It is worthy to note that Dec 1-4, 1969 saw extensive coastal wave wash under neap tide conditions, offset by the surf magnitude on order of 50-100 year turn-around.
Windswell through the period should be minimal from 40-90 degrees. See the latest NWS state weather forecast discussion regarding the gentle local wind pattern of varying direction. Moderate to fresh breezes 1/22 could bring small chop from 180-315 degrees 1/22.
The size of the present and upcoming surf events 1/17-25 can refract waves into most coastal areas of Oahu regardless of orientation.
Surf should increase from the southern hemisphere on Tuesday 1/21 from 190-200 degrees. A severe gale to storm-force fetch set up S to SE of New Zealand 1/13-14. New Zealand shadowed the fetch when winds were strongest. As the associated low cell tracked east clear of the shadow, winds weakened. Only a small episode is expected peaking Wednesday 1/22 from 190-200 degrees.
Into the long range, another fetch set up in a similar location and of similar strength S to SE of New Zealand 1/16-17. However, the head of the fetch reached further north to near 40s, or about 4000 nm away. This should give a notch higher surf locally, building 1/24, peaking 1/25, and dropping 1/26. There could be one more small, long-period event from 190-200 degrees locally 1/28-29.
In the northern hemisphere, extra-large to giant, declining surf from 300-340 degrees is suggested for 1/23. Winter caliber lows are expected to continue forming near 40°N in the NW to central N Pacific, with the next high to extra-large event hinted for 1/24-25 from 305-320 degrees. Minimal windswell from 40-90 degrees should hold 1/23-25.
Long range forecasts are subject to high uncertainty.
This collaborative forecast will resume on Tuesday, January 21.
This forecast was produced through the collaborative efforts of NWS and NCDDC. Please send suggestions to w-hfo.webmaster@noaa.gov or call the Warning Coordination Meteorologist at 808-973-5275.

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