do judge a storm by its cloud cover

Image Credit: NASA Goddard MODIS Rapid Response Team

The rule is don't judge the book by its cover, but in the case of storms, this rule doesn't seem to hold.  Recently, the Philippines encountered what was considered to be the strongest storm ever recorded to make a landfall.  How did they know? In the case of the United States, particularly on matters relating to strong storms in the North Atlantic and the Caribbean, aircraft reconnaissance measurements are performed to measure wind speed and atmospheric pressure.  In the case of the Western Pacific, perhaps except super typhoon Tip in 1979 (considered to be the strongest storm ever recorded in terms of 10-minute maximum sustained winds with the lowest recorded atmospheric pressure, and also the largest storm in terms of diameter), there are no aircraft reconnaissance missions to obtain on-site data about the intensity of the tropical storms especially those storms hovering over ocean waters. Speaking of super typhoon Tip, it has entered the PAR (Philippine Area of Responsibility). It was named Warling by the Philippine weather bureau PAGASA, but it did not make its landfall in the Philippines; it moved to the north direction and hit Japan instead.

Strong typhoons get a lot of attention from satellite surveys; and from the looks of the satellite images of super typhoon Haiyan (locally known as Yolanda), it is considered to be one of the strongest storms that one could ever imagine, judging from its cloud patterns.  So how did they determine the intensity of the storm so that it merits some world record?  We cannot judge a book by its cover, but meteorologists say that we can judge a tropical storm by its satellite images using the Dvorak technique.  Through the Dvorak technique, a forecaster assigns a T-number to a storm after a detailed examination of the satellite images; well, it has some subjective aspects depending on the skill of the forecaster.  However, in the case of a skilled and experienced forecaster, estimates through the Dvorak technique have been found to be reliable through comparisons with the empirical data.  It was developed by Vernon Dvorak between 1969 and 1984, and as time goes on, it has been subjected to improvements such as increasing its objectivity through the automation of the technique.  The current version is known as the Advanced Dvorak Technique and is even more reliable than the previous versions.

Image Credit: 

NASA/SSAI, Hal Pierce

Purple indicates the coldest and most powerful thunderstorms. Note: 273 K = -0.15 deg. Celsius.  
(Image Credit: NASA/JPL-Caltech)

Image Credit: NASA Goddard MODIS Rapid Response Team

Super typhoon Haiyan at its peak intensity (occurring on its first landfall in the Philippines) has been assigned a final T-number of 8.0 in http://www.ssd.noaa.gov/, which means it has winds of about 196 miles per hour or 315 kph (kilometers per hour).  You might be interested on the data found here: 31W-list.txt; and if you examine the raw T-numbers, a T-number of 8.1, which exceeds the upper bound of the scale, has been assigned.  Unofficially, this makes Haiyan the strongest storm ever recorded to make a landfall; and given the recorded 235 kph for 10-minute maximum sustained winds from JMA (Japan Meteorological Agency), it is the second most intense storm ever recorded after super typhoon Tip, which registered 260 kph.  Based on satellite imagery and its characteristics as a storm system, Haiyan is a wonder storm, but unfortunately, this is a destructive natural phenomenon that made its landfall in the Philippines on November 8, 2013.



More on the advanced Dvorak technique here: "The Advanced Dvorak Technique: Continued Development of an Objective Scheme to Estimate Tropical Cyclone Intensity Using Geostationary Infrared Satellite Imagery" by T.L. Olander and C.S. Velden, 2007 [pdf]

Braving the winds of Yolanda:

Image Credit: Ingo Vogelmann