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Thursday, August 19, 2010

Jeff Masters: Massive 926 mb extratropical storm generating huge waves off Antarctica

Massive 926 mb extratropical storm generating huge waves off Antarctica

by Jeff Masters, Wunderblog, August 19, 2010

One of the most intense extratropical storms in recent years is churning up the waters near the coast of Antarctica in the South Indian Ocean. The powerful storm peaked in intensity yesterday afternoon with a central pressure of 926 mb -- the type of pressure typically found in a Category 4 hurricane. Storms this intense form on average once per year, or perhaps less often, according to an email I received from Jeff Callaghan of the Australia Bureau of Meteorology. Since extratropical storms do not form eyewalls, the winds at the surface from this monster storm probably reached "only" 100-120 mph (equivalent to a Category 2 or 3 hurricane). The storm is forecast to generate huge waves with a significant wave height of 13 meters (44 feet) today, according to the NOAA Wavewatch III model (Figure 3).  I have flown into an extratropical storm this intense -- in 1989, I participated in a field project based in Maine that intercepted a remarkable extratropical storm that "bombed" into a 928 mb low south of the Canadian Maritime provinces. You can read my story of that somewhat harrowing flight here.


Figure 3. Satellite image taken at 8:10 UTC, August 19, 2010, showing the intense extratropical cyclone that has weakened to 940 mb in the South Indian Ocean near the coast of Antarctica. Image credit: NASA.


Figure 4. Surface pressure analysis from 18 UTC, August 18, 2010, showing a 926 mb low in the South Indian Ocean, just north of Antarctica. Image credit: Jeff Callaghan, Australia Bureau of Meteorology.


Figure 5. Predicted wave height from the NOAA Wavewatch III model for 2 p.m. EDT (18 UTC) today, August 19, 2010. Peak wave heights of 13 meters (44 feet) are projected over ocean areas between Antarctica and Australia. Long-period waves (19 seconds between crests) up to 7 meters (22 feet) high are predicted to affect the southwest coast of Australia by Sunday. The waves are predicted to propagate eastwards to New Zealand, 8-9 days from now, and be a respectable 4-5 meters high then.


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