The Moore Tornado, and Common Tornado-Hurricane Misperceptions

On May 20, approximately two dozen tornado reports were scattered from Texas into Oklahoma, Kansas, Missouri, and Indiana.  Among them, one in particular combined two deadly ingredients: very intense winds and a populated urban area.  A tornado that struck Moore, OK (a southern suburb of Oklahoma City) was rated an EF5 tornado, with peak winds of 200-210mph.  An EF5 tornado contains the most violent winds on the planet — such winds are capable of leveling virtually any man-made building.

The large-scale setup for a severe weather outbreak was forecast at least a week in advance.  A 2-3 day period of all the necessary ingredients coming together at the same time was anticipated, and the peak threat was expected on May 20.  Indeed, on May 20, a tornado watch was issued for central and eastern Oklahoma at 1:10pm CDT.  Thunderstorms formed about 20 minutes later, and rapidly became severe, rotating supercells.  At 2:40pm, a tornado warning was issued for Moore, then at 3:01pm, a rare tornado emergency was issued.  From approximately 3:15-3:25pm, the massive tornado cut a path of destruction through the city, demolishing everything in its way and killing at least 24 people.

Radar image of the parent supercell that spawned the tornado. This image is from 3:21pm, just as the tornado was tracking through Moore. The magenta-purple blob is called a “debris ball”… rather than the radar beam reflecting off of just hail and rain, it’s also hitting a concentrated airborne ball of debris from houses and other structures. The radar itself is located at the center of the black circle east of Moore.

The tornado that passed directly over Moore was on the ground for 50 minutes and for 17 miles, and was at times about 1.3 miles wide.  This suburban town has been hit by significant tornadoes five times in 15 years: the October 4, 1998 F2, the May 3, 1999 F5, the May 8, 2003 F4, the May 10, 2010 EF4, and now the May 20, 2013 EF5.  (The original Fujita Scale from 1971 was replaced by the more accurate Enhanced Fujita Scale in 2007, and as such, the shorthand tornado rankings switched from F5 to EF5, for example.)  Not surprisingly, the odds of being hit by a significant tornado are climatologically quite high in central Oklahoma in May as seen in this map.

How Do Tornadoes and Hurricanes Compare?

Sometimes people erroneously interchange these two types of storms.  The only thing they have in common is strong winds; outside of that, they are entirely different phenomena.

1) Geography

In the U.S., tornadoes are most commonly found in the Great Plains states, but have been known to occur in almost every state.  They require a parent severe thunderstorm, and a list of atmospheric conditions that is fairly well-known.  If a tornado forms or passes over water, it’s called a waterspout, but for the most part, tornadoes “prefer” land.  Hurricanes, on the other hand, require a warm ocean to form and strengthen.  Once over land, hurricanes quickly weaken.  Only certain islands and coastal areas can be hit by a hurricane, though sometimes side effects can extend further inland (strong winds, flash flooding, tornadoes).

2) Intensity

While both types of storms are capable of producing destructive winds, tornadoes can become stronger than hurricanes.  The most intense winds in a tornado can exceed 300mph, while the strongest known Atlantic hurricane contained winds of 190mph.  The scales used to categorize the two are also different, as shown below.  Tornadoes are ranked on the Enhanced Fujita Scale, while hurricanes are ranked on the Saffir-Simpson Scale.  Beyond about 120mph, winds are powerful enough to significantly damage or destroy structures.

A visual comparison of the scales used for tornadoes and for hurricanes. On the top, the Enhanced Fujita Scale uses three-second wind gusts to define its thresholds. On the bottom, the Saffir-Simpson Hurricane Wind Scale’s thresholds are defined by one-minute sustained winds.

3) Size

While a very large tornado might reach 2 miles across, typically they are much less than a half mile across.  Hurricanes, on the other hand, are several hundred miles in diameter.  Even the eyewall (the inner ring of the most intense winds) is typically about 25 miles across.  Rainbands in the outer circulation of a hurricane can spawn multiple tornadoes simultaneously, while there is no way for the opposite to occur.  Tornadoes are completely dwarfed when it comes to a size comparison.

4) Predictability & Warning

There is also a huge difference in the timescales involved between tornadoes and hurricanes.  While the large-scale environment that is favorable for tornado development can be predicted several days in advance, there is presently no way of predicting individual tornadoes even HOURS in advance.  Once a rotating thunderstorm forms, there is still no way of knowing whether or not it will spawn a tornado, or how strong that tornado will become.  A tornado warning is issued an average of 13 minutes prior to impact, giving people a very limited amount of time to take shelter.  Sometimes that lead time is longer, sometimes shorter.  Conditions that are favorable for hurricane development can also be predicted several days in advance.  But since they usually form over the open ocean, they don’t immediately affect people.  There can be anywhere from a day to well over a week before the storm hits land… if it ever does at all.  Hurricane warnings are issued up to 36 hours before strong winds are expected to affect land, giving people time to prepare themselves and their houses as best they can.  Also due to the difference in time scales, people can evacuate an area prior to a hurricane landfall, but there is no time to evacuate an area before a tornado strikes.

5) Preparation

In both cases, having a plan in place before a storm comes is very important.  When the time comes, putting that plan into action will be stressful enough.  For a tornado, the most critical part of a plan is knowing where you and your family will take shelter; it might be an interior closet or bathroom, a basement, or a storm shelter.  Tornadoes are such short-fuse violent events that you may not have time for much else than protecting life.  Hurricanes are much easier to prepare for and allow for more elaborate planning.  You will have time to protect your house with window coverings, buy supplies, organize important documents, and evacuate if necessary.  If you don’t evacuate, then it’s very similar to a tornado: find the safest location you can to stay for the duration of the storm.  While a tornado will pass over in a matter of seconds or minutes, a hurricane will take several hours to pass over.  In both cases, no shelter is perfect — the most severe tornado or hurricane is capable of such destruction that even the best plan and best shelter may prove insufficient.  But clearly, there are ways to minimize your exposure to danger, and FEMA has some valuable information and resources available at http://www.ready.gov/tornadoes and http://www.ready.gov/hurricanes.

Author: Brian McNoldy,Senior Research Associate in Meteorology and Physical Oceanography at the University of Miami

Hurricane Researcher Brian McNoldy on the Science Behind Sandy

The following interview is featured in Outside Online in a series of interviews about Hurricane Sandy. To read the interview in full, click here.

A video showing Sandy’s life from October 23 to October 31: As Hurricane Sandy moved up the East Coast, a ridge of high pressure north of New Foundland blocked her from moving north and generated clockwise winds that pushed her into the East Coast, where she morphed with a cold front that had been moving east across the Eastern U.S. “The big picture of what made Sandy move north and then curve back northwest was really not having anywhere else to go,” says Brian McNoldy.

It was as a nine-year-old kid in Reading, Pennsylvania, that University of Miami scientist Brian McNoldy developed a fascination with hurricanes. “I think most of us have a storm,” he says. “Mine was Hurricane Gloria, in 1985.”

TV newscasters warned about the impending winds and rain. Local officials cancelled school for a few days. When the storm hit, it knocked out power. McNoldy went outside. “I can still remember how strong the winds were,” he says. “We didn’t get hit by the eyewall—just by the rainbands, but even that was pretty impressive.”

After earning undergraduate degrees in physics and astronomy at Lycoming College, a graduate degree in atmospheric science at Colorado State University, and picking up research experience at Colorado State University, he landed at the University of Miami in January of 2012. “This is an up-and-coming school in hurricane research, and there’s a lot of momentum going here,” he says. “I’m happy to have the opportunity to be part of it.”

For his job, he works on something called “vortex initialization code” for a joint project with the Navy. It’s a series of sophisticated computer programs that allow scientists to take a crudely-represented hurricane out of a model analysis, replace it with a more realistic hurricane that has tuneable factors (such as intensity, size of the storm, etc.), and see how changes affect the forecast.

When he’s not working on the vortex code, he writes about hurricanes. “I started what, at the time, wasn’t called a blog, because they weren’t really there yet, in 1996,” he says. “For any storm—not even a storm, for any wave in the Atlantic, I would have my little list of people who were interested in what was going on, and I would send updates to them during hurricane season. I’ve been doing that for 16 years now.”

His audience has grown. From 2007 to 2010, he was invited to blog about hurricanes for The New York Times. In 2012, he started blogging for the Washington Post and the Rosenstiel School of Marine and Atmospheric Science. On October 22, when Sandy was still Tropical Depression 18, he was one of the first to report on the likelihood of it turning into the Northeast U.S. with possibly devastating consequences. We caught up with him to learn a bit more about the science behind Sandy.

When did you start watching Sandy?
I think some of the models were picking up on something forming in the Western Caribbean probably by about October 12 or 13. Some models picked up, run after run, something that would form in the Western Caribbean, and then would move north toward Cuba. That persisted and they ended up being right. The National Hurricane Center issued the first advisory on Tropical Depression 18 on October 22, then upgraded it to Tropical Storm Sandy later the same day. It eventually headed north over Jamaica and Cuba. I thought, Wow, that’s extremely impressive for those models.
[Editor’s Note: Models are computer programs used to help forecast the formation and movement of tropical storms and hurricanes.]

On October 22, you blogged that there was a possibility it could hit the East Coast. How did you know that?
There are a few rather reliable global models. They’re models that run all the time, all year long, so they don’t focus on any one storm. They run for the entire globe, not just for North America. There are two types of runs these models can be configured to do. One is called a deterministic run and that’s where you get one forecast scenario. Then the other mode, and I think this is much more useful, especially at longer ranges where things become much more uncertain, is ensemble—where 20 or 40 or 50 runs can be done. They are not run at as high of a resolution as the deterministic run, otherwise it would take forever, but it’s still incredibly helpful to look at 20 runs.

Because you have variation? Do the ensemble runs include different winds, currents, and temperatures?
You can tweak all sorts of things to initialize the various ensemble members: the initial conditions, the inner-workings of the model itself, etc. The idea is to account for observational error, model error, and other sources of uncertainty. So you come up with 20-plus different ways to initialize the model and then let it run out in time. And then, given the very realistic spread of options, 15 of those ensemble members all recurve the storm back to the west when it reaches the East coast, and only five of them take it northeast. That certainly has some information content. And then, one run after the next, you can watch those. If all of the ensemble members start taking the same track, it doesn’t necessarily make them right, but it does mean it’s more likely to be right. You have much more confidence forecasting a track if the model guidance is in in good agreement. If it’s a 50/50 split, that’s a tough call.

To read the rest of the interview, click here.

Do you have any questions for Brian about Sandy or other Hurricanes? Leave them in the comments section below.

Joe Spring
Outside Magazine
Follow Joe on Twitter: @JoeSpring

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Potential Big Storm For Northeast U.S. Next Week

Just eight days after Sandy’s historic landfall near Atlantic City flooded hundreds of miles of coastline, and left nearly 8 million people without power, the Northeast U.S. could be in for another dose of Nature’s fury by the middle of next week.

Weather models are in agreement on a significant storm shaping up early in the week, then heading northeast along the coast and into New England. Unlike Sandy, this storm won’t have a name or tropical origins, but rather, fit the typical Nor’easter mold.

Two model’s depiction of the surface winds next Wednesday afternoon. The approximate track of the Low pressure from the Carolinas to its position on Wednesday is overlaid.

This storm will almost certainly *NOT* bring the same level of disastrous impacts to the region, but could easily bring unwelcome heavy rain and snow, strong winds, and of course, storm surge and coastal flooding from North Carolina all the way up to Maine -including New Jersey and New York. People in these areas are no strangers to potent Nor’easters, but they usually don’t have to face one immediately after a hurricane.

I will continue to monitor the long-range models for changes, but when the leading ones agree on something just five days away, it is a good sign that they’re onto something.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Superstorm Sandy Managed to Live Up to the Hype

For many, Sandy certainly lived up to the seemingly impossible forecasts of impacts. For starters, it made landfall with a central pressure of 946mb – the second lowest pressure ever recorded for any storm to hit the northeastern U.S. (first place was the 1938 Great New England Hurricane at ~941mb). Maximum sustained winds were 80mph, and higher gusts were reported from Rhode Island down to North Carolina.

The center came ashore near Atlantic City, NJ around 8pm EDT last night, though its effects were of course felt far from the center. This satellite image above shows Sandy at landfall on Monday evening.

In terms of a human toll, 84 lives have been taken by the storm (as of 9am Tuesday morning) across the Caribbean, the U.S., and Canada.

At least 7.5 million people in the northeast are without power. The only silver lining there is that the temperatures after the power outages aren’t sweltering or frigid, so it’s generally not as life-threatening as it could be.

The Battery in downtown NYC ended with a peak water level of 13.88′, which is about 2’8″ higher than the previous record (set in 1821). That, of course, resulted in a total catastrophe. By around 8pm, the subways and automobile tunnels were filling with sea water. And before that, both JFK and La Guardia airports had flood water pouring across the runways and into the terminals. The flooded areas of NYC also experienced large fires, collapsed buildings, and the power company shut off electricity to the city before the flooding got too bad and damaged the equipment. The iconic fishing pier at Ocean City, MD has been completely destroyed. The streets of Wildwood, NJ became the beach as the storm surge inundated the huge beach they used to have. The Atlantic City boardwalk is now rubble and the city flooded. The full range of impacts across all of the states are too numerous to detail here, but you will undoubtedly see and read more in the news.

A buoy at the entrance to the New York Harbor recorded a peak wave height of 32.5 feet, but I’m not yet aware of what affects such large waves had on the immediate area.

As of this morning, the Potomac River reached its highest level since 1996 due to the heavy rainfall. 5-7″ of rain fell in much of Maryland, Delaware, and northern Virginia; southern New Jersey received about 7-9″, northern New Jersey saw about 2-4″, while much of southest Pennsylvania was in the 3-5″ ballpark. Meanwhile, it’s still snowing hard West Virginia and they are expecting 2-3 feet of very wet snow.

It’s not over yet either. Heavy rain is still falling over an enormous area, and storm surge and coastal flooding continues to be a very large danger. This image shows the current radar depiction of the precipitation still affecting 17 states. I also have very long radar loops covering Sandy available: click here

Sandy will certainly be a storm for the record books, and will also end up being a retired name. Going back to 1953, the only storms so late in the alphabet to be retired were Stan (2005), Wilma (2005), and Tomas (2010).

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Hurricane Sandy Expected to Make Historic Landfall Tonight

Hurricane Sandy continues to loom ominously off the U.S. east coast, bringing very heavy rain and tropical storm to hurricane force winds to many millions of people well before the worst arrives. The coastal flooding is already terrible, as expected (even as far south as Miami and Fort Lauderdale!). Locations from North Carolina to Maine will continue to see incredible coastal flooding/erosion, with the worst near and north of where the center crosses land (approximately southern NJ into NYC, Long Island, CT, RI, and MA). Inland flooding will also be a large problem in the coastal states as well as the inland states throughout the northeast. Finally, the 50-90mph winds that many places will experience can easily damage roofs, break tree limbs, and uproot trees, bringing power lines down with them.

At 8am EDT today, Sandy was a Category 1 hurricane with 85mph sustained winds, and a 946mb central pressure (it’s that very low pressure that creates the strong winds at the surface). The wind field is so large that tropical storm force winds (45mph+) extend 485 miles out from the center. The center is located approximately 300 miles south of NYC and 300 miles east of Norfolk – heading for a landfall late tonight near the Delaware Bay area. I have multiple long radar loops available at: click here.

Perhaps the trickiest part of this system from a warning perspective is that Sandy may not technically be a hurricane by the time it reaches the coastline later tonight. It is interacting with a cold front that is draped on the coastline and is losing some of its tropical characteristics. It actually has a warm front forming off to its east and a cold front to its south – a sign that it’s transitioning to an extratropical cyclone.

This absolutely does not make it any less dangerous! It has been intensifying (by both tropical AND extratropical mechanisms), and this interaction with the mid-latitude front is exactly what has been forecast to occur for days now. With or without a hurricane or a hurricane warning, this storm is extraordinary, unprecedented, and must be taken very seriously. The storms it has been compared to are the 1938 Great New England Hurricane, Hurricane Gloria in 1985, and the “Perfect Storm” of 1991. Sandy will join this crowd, and likely surpass some (if not all) of them in total impacts and damage.

This is truly a worst-case scenario that will cost many billions of dollars and claim hundreds of lives. Huge unthinkable storm surges along the entire northeast U.S. coast, mostly reaching their worst at night and during a full moon (already higher-than-normal tides), large rainfall amounts over several states, 2-3 FEET of wet snow in the mountains of WV, and widespread power outages for perhaps 10 million people.

If you’re in the affected areas, be aware of nearby streams/creeks/rivers that could quickly turn into white water rivers, large trees near your house, and be prepared to lose power for several days. Also, remember to check up on family and friends who might be at a higher risk than you.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Sandy’s Historic Encounter with the Northeast U.S. Looking Very Likely

Hurricane Sandy formed just four days ago north of Panama. In its short lifetime so far, it has claimed 21 lives in Jamaica, Haiti, and Cuba and unexpectedly intensified to a strong Category 2 storm immediately after exiting mountainous eastern Cuba. It passed over the central Bahamas on Thursday with 105mph sustained winds, and brought tropical storm conditions to Miami, West Palm Beach, and the southeast Florida peninsula. Today, conditions over southern Florida are improving as Sandy crawls north at 6mph. As of 11am this morning, Sandy’s maximum sustained winds are 80mph (a Category 1 hurricane) and the wind field is expanding. Tropical storm force winds (35mph+) now reach 275 miles from the storm’s center, and weaker though still noteworthy winds extend approximately 800 miles from the center. It is located 190 miles due east of West Palm Beach, FL.

The official track from the National Hurricane Center shows Sandy moving slowly to the north through Saturday, then northeast for a couple of days before getting pulled back westward toward the coast. Tropical storm watches and warnings are in effect for the U.S. east coast from the southern tip of Florida to the Outer Banks of North Carolina.

The longer range forecast is becoming more certain as nearly every model now agrees on a similar track and evolution. Unfortunately, the solution being converged upon is a devastating and historic “perfect storm” scenario for the entire northeast U.S. from the coast to hundreds of miles inland.

There’s a fine line between over-hyping a situation, and giving plenty of advanced warning prior to a potentially catastrophic situation. When it comes to a forecast for something like this, think of a spectrum of possibilities: a chance that it won’t be so bad and all the hype is overkill, a chance that it will live up to or even exceed the hype, and then the middle ground of a bad storm, but nothing to panic about. Of course, we don’t know with 100% certainty which of these possibilities will be realized, but since the high-end impact scenario is presently a very real one, it would be prudent to over-prepare and be safe than under-prepare and regret it.

In an effort to aid forecasters as much as possible, weather balloons are being released four times per day rather than the typical two times per day across the entire nation. These enhanced upper-air observations upstream of the storm are fed into models, and starting with more accurate knowledge of the true state of the atmosphere would ideally lead to more accurate forecasts. Secondly, there are two aircraft flying around in the storm this morning: one from NOAA’s Hurricane Research Division and one from the Air Force’s Hurricane Hunter fleet. This will help guide storm-scale data assimilation, while the additional weather balloons will help with large-scale environmental data assimilation. These resources are being utilized due to the looming “perfect storm” scenario unfolding over the next few days.

From Sunday through the middle of next week (and beyond?), this system is forecast to intensify while expanding at the same time. This would bring extraordinary storm surge and rainfall to the entire mid-Atlantic and northeast U.S. regions. If you lived in those areas during Irene last year, consider that a practice run. This setup is truly rare and is not your typical hurricane or Nor’easter riding up along the coast.

Several days of heavy rain combined with the strong wind can easily result in widespread flooding, tree damage, and power outages. The Monday-Tuesday period should be core of the worst weather in the northeast, but it won’t just end abruptly either. Immediately along the coast, very high storm surges combined with beach erosion could lead to significant seawater flooding. The full moon on Monday will make the normal high tides even higher, and raising the base sea level.

We will have another update tomorrow when Sandy is located east of Georgia and South Carolina and about one day prior to impacts being felt in the majority of the mid-Atlantic region.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy