Blog Archive

Saturday, November 16, 2013

Jeff Masters: Haiyan's true intensity and death toll still unknown

by Jeff Masters, wunderblog, November 15, 2013

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 3,432 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 5,081-8,165 people. Damage is estimated at $12-$15 billion, or about 5% of the Philippines' GDP.

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.

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 (11.2414 N, 125.0036 E). This location was about 18 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 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 a.m., and their Device 2 measured 960.3 mb at 7:20 a.m. 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.

Figure 2. Pressure observed in downtown Tacloban during the passage of Super Typhoon Haiyan on November 8, 2013, by Josh Morgerman of This sensor bottomed out at 960.3 mb at 7:20 a.m., at a location a few miles north of the northern edge of the eye. If we look at the Tacloban airport pressure readings in the last 3 hours they sent data on November 8, the readings were 1001.1 mb, 1000.9 mb, and 997.3 mb, at 12 a.m., 1 a.m., and 2 a.m., respectively. The iCyclone instrument recorded 1002 mb, 1000 mb, and 998 mb at those times, so the two instruments agreed to within 1 mb.

Figure 3. Radar image of Super Typhoon Haiyan over Tacloban, on November 8, 2013. Tacloban was in the north (strongest) portion of Haiyan's eyewall, at a time when the typhoon's top sustained winds over water were estimated at 185 mph. Image credit:

How strong were Haiyan's winds at initial landfall in Guiuan?
Haiyan's strongest winds occurred on the south shore of Samar Island and the city of Guiuan (population 47,000), where the super typhoon initially made landfall with 1-minute average winds estimated at 195 mph. This estimate came from the Joint Typhoon Warning Center (JTWC), and was based on satellite measurements. We have no ground level or hurricane hunter measurements to verify this estimate. The Japan Meteorological Agency (JMA), which uses their own techniques to estimate typhoon strength via satellite imagery, put Haiyan's peak strength at 125 knots (145 mph), using a 10-minute averaging time for wind speeds. The averaging time used by JTWC and NHC is 1-minute, resulting in a higher wind estimate than the 10-minute average winds used by JMA and PAGASA in their advisories. To convert from 10-minute averaged winds to 1-minute average, one conversion factor that is commonly used is to multiply by 1.14 -- though lower conversion factors are sometimes used. JMA satellite strength estimates are consistently much lower than those from JTWC for high-end Category 5 strength typhoons; JTWC estimates are the ones most commonly used by the hurricane research community. A searchable database going back to 1976 of the JMA typhoon information available at Digital Typhoon reveals that Haiyan is tied for second place as the strongest typhoon that JMA has rated, and was the strongest landfalling typhoon, when measured by wind speed. The only typhoon they rated as stronger was Super Typhoon Tip of 1979, but that storm weakened to Category 1 strength before making landfall in Japan. 

Figure 4. The 400-year-old Church of the Immaculate Conception (left) collapsed in Guiuan, Philippines, during Super Typhoon Haiyan. Image credit: J.B. Baylon and

Typhoon and hurricane maximum wind speed estimates are only valid for over water exposure, and winds over land are typically reduced by about 15%, due to friction. This would put Haiyan's winds at 165 mph over land areas on the south shore of Samar Island. This is equivalent to a high end EF-3 tornado. 

Forty minutes before landfall, the airport in Guiuan reported sustained 10-minute average winds of 96 mph, with a pressure of 977 mb, before contact was lost. Damage photos of Guiuan show at least EF-2 scale damage (111-135 mph winds): Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. The mayor of the city had his car lifted off the ground and slammed into a building, which is consistent with at least EF-2 damage. 

There is possible EF-3 damage (136-165 mph winds) in the Guiuan damage photos, with the 400-year-old stone Church of the Immaculate Conception collapsed, and a bus toppled. EF-3 damage is defined as: Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance. A detailed damage survey would be need to determine if EF-3 winds really did occur in Guiuan. 

Haiyan Links
Wunderblogger Lee Grenci discusses mesovorticies in the eye of Haiyan in his latest post.
Wunderground's weather historian Christopher C. Burt reviews the Philippine's typhoon history.
The University of Wisconsin CIMSS Satellite Blog has a great collection of satellite images of Haiyan.
NOAA's Michael Folmer has a post showing the unusual burst of lightning that occurred at landfall in Haiyan.
Hurricanes and Climate Change: Huge Dangers, Huge Unknowns, my August 2013 blog post.
Storm Chaser James Reynolds on Twitter, from Tacloban, Leyte.
Storm Chaser Jim Edds on Twitter, from Tacloban, Leyte.
Storm Chaser Josh Morgerman (iCyclone) on Facebook

The Philippine Red Cross is appealing for donations.

Portlight disaster relief charity is reaching out to disability organizations in the Philippines to provide durable medical equipment. and welcomes donations.

Figure 5. "Tipping Points" host Bernice Notenboom goes on a sled adventure in Greenland.

New "Tipping Points" episode, "Greenland Ice-sheet Melt," airs Saturday at 9 p.m. EDT, 8 p.m. CDT 

“Tipping Points,” the landmark 6-part climate change TV series that began airing in October on The Weather Channel, airs for the fifth time on Saturday night, November 16, at 9 p.m. EDT. The new episode, "The Greenland Ice-sheet Melt," goes on an expedition to the remote Inuit village of Qaanaaq to explore the rate Greenland Ice sheet melt and its effects on global ocean circulation. I make a short appearance 8 minutes into the episode to report on how much ice Greenland has lost in the past decade. The series is hosted by polar explorer and climate journalist Bernice Notenboom, the first woman to perform the remarkable triple feat of climbing Mt. Everest and walking to the North and South Poles. In each episode, Notenboom heads off to a far corner of the world to find scientists in the field undertaking vital climate research to try to understand how the climate system is changing and how long we have to make significant changes before we reach a tipping point--a point of no return when our climate system will be changed irreversibly.

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