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WEST COAST TSUNAMI ADVISORY IN EFFECT
Samoa earthquake generates Pacific-Ocean-wide Tsunami
By:
Sean Collins
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September 29, 2009
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As of approx. 5pm Pacific Time, an official Tsunami Advisory has been issued for the California + Oregon coasts,
and would certainly include Mexico and Baja. A 5-foot Tsunami was recorded in Samoa, which created some damage there close to the tsunami source.
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Previous
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A small, one-foot tsunami did pass through Hawaii at about 3:00 Hawaii time, and is expected to begin to arrive along the Pacific West Coast around 9:00 PM this evening Pacific Time. As you can see from the tsunami propagation chart on right, more energy did appear to be sent toward the Pacific West Coast compared to Hawaii, so the tsunami may be a little larger on the Pacific West Coast. The size of the tsunami is not expected to be very large along the Pacific West Coast, and official estimates are about 1-2 feet above normal sea level. But remember, that would result in a possible 2-4 foot tidal wave. That is not a large wave compared to our normal "surfable" gravity waves, but the difference is a tsunami wave has no back of the wave. So it is more of a tidal surge of water than an actual wave. There will likely be 4-6 waves, with the largest waves between the 2nd and 5th waves. The water normally recedes before these waves arrive, so if by chance you're on the beach and see the tide drop significantly all of a sudden, head for high ground immediately. However, with this small tsunami, if a person is standing on a normal beach the tsunami may be barely noticeable other than a period of larger waves surging a little farther up on the beach. We do have a 5.1 high tide in Southern California about 7:00 so the medium high tide will be on its way down. The most prominent effects of the tsunami may be a large amount of abnormal surging of water, especially around areas where the surging water could be somewhat restricted, trapped, or pooled. These areas might be near the entrances of all harbors open to the southwesterly direction. In these areas we see a significant amount of surging from the extra water washing in and out at about 4 minute intervals from 9:00 to about Midnight along the Pacific West Coast. Marine interests should double check their moorings and properties to confirm they are properly secured against surging and a possible 2-4 foot rise and fall in tide. Beachgoers should use extra caution, and due to all the unknown possible factors should probably stay off the beach. The most dangerous areas will be near water restricted areas like harbor entrances where surging, wave, and water heights will all be magnified. Please stay tuned to NOAA, local radio and TV stations, and local authorities for the latest information. Once again, this is not expected to be a significant tsunami but there are a lot of unknowns and everyone should use extra caution. +++ PUBLIC TSUNAMI MESSAGE NUMBER 5 NWS WEST COAST/ALASKA TSUNAMI WARNING CENTER PALMER AK 521 PM PDT TUE SEP 29 2009 ...A TSUNAMI ADVISORY IS IN EFFECT WHICH INCLUDES THE COASTAL AREAS OF CALIFORNIA AND OREGON FROM THE CALIFORNIA-MEXICO BORDER TO THE OREGON-WASHINGTON BORDER... A TSUNAMI ADVISORY MEANS THAT A TSUNAMI CAPABLE OF PRODUCING STRONG CURRENTS OR WAVES DANGEROUS TO PERSONS IN OR VERY NEAR THE WATER IS IMMINENT OR EXPECTED. SIGNIFICANT WIDESPREAD INUNDATION IS NOT EXPECTED FOR AREAS UNDER AN ADVISORY. CURRENTS MAY BE HAZARDOUS TO SWIMMERS... BOATS... AND COASTAL STRUCTURES AND MAY CONTINUE FOR SEVERAL HOURS AFTER THE INITIAL WAVE ARRIVAL. AT 1048 AM PACIFIC DAYLIGHT TIME ON SEPTEMBER 29 AN EARTHQUAKE WITH PRELIMINARY MAGNITUDE 8.0 OCCURRED IN THE SAMOA ISLANDS REGION. THIS EARTHQUAKE HAS GENERATED A TSUNAMI WHICH COULD CAUSE DAMAGE TO REGIONS IN A WARNING OR ADVISORY. ESTIMATED TSUNAMI ARRIVAL TIMES AND MAPS ALONG WITH SAFETY RULES AND OTHER INFORMATION CAN BE FOUND ON THE WEB SITE WCATWC.ARH.NOAA.GOV. A TSUNAMI HAS BEEN OBSERVED AT THE FOLLOWING SITES LOCATION LAT LON TIME AMPL ------------------------ ----- ------ ------- ----------- APIA WEST SAMOA 13.8S 171.8W 1832UTC 0.70M/2.3FT PAGO PAGO AMER. SAMOA 14.3S 170.7W 1825UTC 1.57M/5.1FT RAROTONGA COOK IS. (NZ 21.2S 159.8E 1950UTC 0.54M/1.8FT PAPEETE FR. POLYNESIA 17.5S 149.6W 2137UTC 0.14M/0.5FT PENRHYN COOK IS. NZ 9.0S 158.0W 2103UTC 0.08M/0.3FT PORT VILA VANUATU 17.8S 168.3E 2239UTC 0.18M/0.6FT NAWILIWILI KAUAI HI 22.0N 159.4W 0011UTC 0.16M/0.5FT KAWAIHAE HI 20.0N 155.8W 0013UTC 0.18M/0.6FT FORECASTS INDICATE THAT A TSUNAMI WITH AMPLITUDES IN THE RANGE OF 6 TO 24 INCHES (20 TO 65CM) IS EXPECTED ALONG THE CALIFORNIA AND OREGON COAST. TSUNAMIS OF THIS AMPLITUDE CAN GENERATE STRONG CURRENTS DANGEROUS TO THOSE VERY NEAR OR IN THE OCEAN. THE TSUNAMI IS EXPECTED TO BUILD AND REACH ITS MAXIMUM APPROXIMATELY ONE AND A HALF HOURS AFTER THE INITIAL ARRIVAL. TSUNAMIS CAN BE DANGEROUS WAVES THAT ARE NOT SURVIVABLE. WAVE HEIGHTS ARE AMPLIFIED BY IRREGULAR SHORELINE AND ARE DIFFICULT TO FORECAST. TSUNAMIS OFTEN APPEAR AS A STRONG SURGE AND MAY BE PRECEDED BY A RECEDING WATER LEVEL. MARINERS IN WATER DEEPER THAN 600 FEET SHOULD NOT BE AFFECTED BY A TSUNAMI. WAVE HEIGHTS WILL INCREASE RAPIDLY AS WATER SHALLOWS. TSUNAMIS ARE A SERIES OF OCEAN WAVES WHICH CAN BE DANGEROUS FOR SEVERAL HOURS AFTER THE INITIAL WAVE ARRIVAL. DO NOT RETURN TO EVACUATED AREAS UNTIL AN ALL CLEAR IS GIVEN BY LOCAL CIVIL AUTHORITIES. THE TSUNAMI MESSAGE WILL REMAIN IN EFFECT UNTIL FURTHER NOTICE. FOR FURTHER INFORMATION STAY TUNED TO NOAA WEATHER RADIO... YOUR LOCAL TV OR RADIO STATIONS... OR SEE THE WEB SITE WCATWC.ARH.NOAA.GOV MORE SURF NEWS SURFLINE HOME PAGE |