Wunderground.com by Dr. Jeff Masters Blogs
Figure 1. Infrared VIIRS image of the eye of Haiyan taken at 16:19 UTC November 7, 2013. At the time, Haiyan was at peak strength with 195 mph sustained winds. Image credit: NOAA/CIRA.
A full week after one of the strongest tropical cyclones in world history devastated the Philippines, the full extent of the death and destruction wrought by Super Typhoon Haiyan is still not fully known, nor do we have actual ground measurements of the storm's peak winds and lowest pressure. The Philippines National Disaster Risk Reduction and Management Council estimates 3432 people were killed, and the U.N. puts this number at 4,460. This makes Haiyan the 2nd deadliest Philippines tropical cyclone in history, behind Tropical Storm Thelma of 1991, which killed 5081 - 8165 people. Damage is estimated at $12 - $15 billion, or about 5% of the Philippines' GDP.
What was Haiyan's lowest pressure?
The Japan Meteorological Agency (JMA) estimated that Haiyan's central pressure was 895 mb at landfall, which would make it the 12th strongest tropical cyclone in world history (by pressure.) We now have pressure measurements from Haiyan's second landfall in Tacloban, where a group of storm chasers deployed two high-quality Kestrel pressure instruments in the Hotel Alejandro, in the heart of the Downtown district (11.2414N 125.0036E.) This location was about eighteen miles north of the center of the eye, and did not receive the typhoon's strongest winds, which probably occurred about two miles to the south, judging by the zoomed-in radar image from landfall (Figure 3.) Josh Morgerman of iCyclone.com was kind enough to send me plots of the data recorded from their instruments. Device 1 measured a minimum pressure of 960.8 mb at 7:12 am, and their Device 2 measured 960.3 mb at 7:20 am. Josh talked to a source at the Tacloban Airport, located about 1 mile farther to the south, who said that the airport measured 955.6 mb at 7:15 am, before power was lost. These readings suggest that Haiyan had a pressure gradient of about 4 mb per mile. If we assume the airport was 17 miles north of the center of the eye, and there was a 4 mb/mile pressure gradient, Haiyan could have had an 888 mb central pressure. An email I received from NHC hurricane specialist Dr. Jack Beven documented several cases of Category 5 tropical cyclones with extreme pressure gradients:
Hurricane Andrew, 1992 (South Florida): 60 mb in 14 miles (4.3 mb/mile)
Hurricane Wilma, 2005 (in Caribbean): 94 mb in 14 miles (6.7 mb/mile)
Super Typhoon Megi, 2010 (east of Philippines): 60 mb in 14 miles (4.6 mb/mile)
September 1933 hurricane (ship measurement): 45 mb in 6 miles (7.5 mb/mile)
Hurricane Felix, 2007 (in Caribbean): 63 mb in 14 miles (4.5 mb/mile)
So, it is certainly possible that Haiyan had a pressure below 900 mb, but we will probably never know for certain.
