Super Typhoon Haiyan: How intense and how do we know?
Super Typhoon Haiyan, called Yolanda in the Philippines, was the 13th named storm of the 2013 Pacific typhoon season and is now unofficially the strongest recorded tropical cyclone to make landfall. It likely hit the central Philippines with sustained winds around 180-195 miles per hour (mph) with wind gusts near 225 mph on November 7, 2013.
Today, in the aftermath of the storm, the Philippines is facing some extreme challenges. It’s now estimated that over 10,000 people are dead with many more missing. A tropical disturbance has been pushing through the country today (November 12, 2013), providing heavy rains and gusty winds. Although this system is not strong, it is disrupting recovery efforts. A big worry now is disease, as dead bodies remain on roads, bridges and in the rubble. Finding fresh water and food to the disaster areas present a major challenge, and these problems are bound to continue for several weeks if not months. Follow the links below to learn more about Haiyan.
How Haiyan became classified with winds of 195 mph. In the Western Pacific, we do not have hurricane hunters to fly out into storms to measure wind speeds or pressures. Since we cannot physically record these measurements, we must rely on satellite data to determine the intensity of the storm.
We use a scale called the “Dvorak” technique. It uses a variety of measurements to determine the intensity of the storm. It measures the intensity of the storm from a scale of 0.0 to 8.0. A Dvorak rating of 2.0 typically shows a tropical depression (weak storm) and a rating of a 3.5-4.0 typically shows a storm at hurricane/typhoon intensity. According to NOAA:
Utilizing the current satellite picture of a tropical cyclone, one matches the image versus a number of possible pattern types: Curved band Pattern, Shear Pattern, Eye Pattern, Central Dense Overcast (CDO) Pattern, Embedded Center Pattern or Central Cold Cover Pattern. If infrared satellite imagery is available for Eye Patterns (generally the pattern seen for hurricanes, severe tropical cyclones and typhoons), then the scheme utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops. The larger the difference, the more intense the tropical cyclone is estimated to be.
So why do I mention the Dvorak technique? Super Typhoon Haiyan was so strong, the Dvorak rating was around a 8.1, breaking the highest measurement typically seen. This technique estimates a storm of 8.0 to have a barometric pressure around 858 millibars (mb). Could this have been the pressure of Haiyan? We will never truly know, but the technique works, even though there are fluctuations and estimates within the classifying system.
As of now, Haiyan is considered to officially have a pressure of 895 mb. Remember, the lower the pressure, the stronger the storm. The lowest pressure ever recorded in the world was from Super Typhoon Tip in 1979. Reconnaissance aircraft measured a pressure of 870 mb.
Lightning in the core of Super Typhoon Haiyan? Prior to making landfall, Haiyan appeared to have an increase in lightning activity around the eye wall. Lightning is not very common in tropical cyclones. According to NOAA:
Surprisingly, not much lightning occurs in the inner core (within about 100 km or 60 mi) of the tropical cyclone center. Only around a dozen or less cloud-to-ground strikes per hour occur around the eyewall of the storm, in strong contrast to an overland mid-latitude mesoscale convective complex [your typical storms over land] which may be observed to have lightning flash rates of greater than 1000 per hour maintained for several hours.
This lack of inner core lightning is due to the relative weak nature of the eye wall thunderstorms. Because of the lack of surface heating over the ocean and the “warm core” nature of the tropical cyclones, there is less buoyancy available to support the updrafts. Weaker updrafts lack the super-cooled water (e.g. water with a temperature less than 0° Celsius or 32° Fahrenheit) that is crucial in charging up a thunderstorm by the interaction of ice crystals in the presence of liquid water (Black and Hallett 1986). The more common outer core lightning occurs in conjunction with the presence of convectively-active rainbands (Samsury and Orville 1994).
With this in mind, it was unusual to see an increase in lightning activity with Haiyan. It is likely the interaction with land could have brought upon more lightning activity near the core of the system. However, it is potentially a sign that the storm was intensifying. When storms become as strong as Haiyan, they typically undergo eye wall replacement cycles. When they do that, the original eye becomes ragged and redevelops. As this occurs, the system typically weakens, reorganizes, and tries to become stronger over the next 12-24 hours. Oddly, Haiyan was so strong, any cycles that did form did not affect the cyclone. It maintained intensity, and in fact, likely strengthened as it made landfall. Increase in lightning activity raises eyebrows, and it looks like a great topic of research for a meteorologist.
How intense was Haiyan at landfall? There is no doubt that Haiyan made landfall as a Category 5 storm with winds much higher than the predefined lower limit of 159 mph. In the image above, you can see that rainfall rates increased as the storm approached the Philippines.
There two possible reasons for the increase in rainfall. First, the interaction between Haiyan and land could have created more lift and a higher chance for heavy rain to fall in the Philippines. Second, there is plenty of speculation that increased rainfall rates from tropical cyclones can indicate intensifying cyclones.
In other words, we saw increased lightning and increased rainfall rates as Haiyan made landfall. What does that mean? I think there’s a good shot that this storm was intensifying prior to landfall. Of course, there will be plenty of research for meteorologists to determine whether or not this was the case. However, based on satellite visuals and data that has come in, it would not surprise me if I am right about this.
The Central Command, AFP shared some horrific images as they flew over Guian in the Philippines. Here’s what they said:
A PAF Nomad aircraft flew over Guian, Esamar this morning from 1030H to 1045H. These are the pics we took. Guian bore the brunt of Super Typhoon Haiyan (Yolanda) at its first landfall last Friday. One hundred percent of the structures either had their roofs blown away or sustained major damage. Nearly all coconut trees fell. We saw people in the streets, seemingly dazed. Trucks and cars were left in the streets where they were stopped in their tracks as Yolanda struck. We were probably the first outsiders to fly over the area since Friday and obviously, no relief goods have arrived there yet. It was almost lunchtime but there was no smoke from cooking fires. The 2.4 km runway is clear of debris and could still be used by C130 aircraft. Yolanda is probably worse than Pablo and the only reason why we have no reports of casualties up to now is that communications systems in Region 8 are down … – Col John Sanchez
Bottom line: Super Typhoon Haiyan produced over 190 mph winds and storm surge of 15-20 feet across the central Philippines. It is estimated that over 10,000 people are dead with many more missing. The Philippines are desperate for clean water, food, and shelter. Hundreds of thousands of people are dislocated, confused, and starving. Disease could become an issue over the next several weeks. The scenes are gruesome, horrible, and unbelievable. It is likely that Super Typhoon Haiyan was the most powerful tropical cyclone to ever hit land in the world since record keeping began. I think there’s a shot that Haiyan intensified prior to landfall as rainfall and lightning activity increased (granted, interaction with land can help create this too). Regardless, this was one of Mother Nature’s most powerful storms ever recorded. Unfortunately, it hit a vulnerable area that could take months to years to recover.