Just How Unprecedented Was Hurricane Sandy?

Mean sea level pressure for 0600 UTC October 29, 2012 (contoured) with standard deviations from normal (shaded). Image courtesy Pennsylvania State Meteorology Department.

The first question we ask is: just how unprecedented was Hurricane Sandy? While the Perfect Storm of 1991 is a good analogue in terms of meteorological setup, it did not have nearly the kind of impacts Sandy produced over the Mid-Atlantic states and Long Island since it developed much further out to sea. The historical record shows that there have been other hurricanes to affect the northeastern United States. Notable examples include Hurricane Donna of 1960, Hurricane Carol of 1954, the Great New England Hurricane of 1938, the New York Hurricane of 1893, and the Norfolk and Long Island Hurricane of 1821. While these hurricanes have been classified as being fully tropical, it is difficult to know for sure about those that occurred during the pre-satellite era. Limited data we have suggests that the 1938 hurricane was perhaps an event similar to Sandy in terms of baroclinic enhancement of a tropical system. In either case, a “Sandy-like” event appears to occur no more than once every 50-100 years. Another unique and ultimately devastating attribute about Sandy is that she had the highest Integrated Kinetic Energy (IKE), a measure that combines size and strength of the wind field, of any tropical system on record with almost 4 times the IKE of Hurricane Katrina. The high IKE associated with Sandy can be primarily attributed to the storm’s incredible size. Lastly, the minimum sea level pressure field associated with Sandy was less than 9 standard deviations below normal while off the Mid-Atlantic coast, confirming that Sandy was perhaps a once-in-a-lifetime event.

NHC track forecast errors, courtesy NOAA.

While Sandy was both historic and disastrous for the Northeast, there was one other historic side of the story that is actually positive: the forecasts for the track of Sandy were spot-on. For perspective, 5-day National Hurricane Center (NHC) forecast track errors back in 1970 were 518 mi, which would have encompassed the entire shoreline from southern South Carolina through northeast Maine. Even in 1990, 5-day forecast errors were still 345 mi, which encompasses everything from southern North Carolina through northern Massachusetts. For Sandy, NHC forecasted a landfall near Atlantic City, NJ five days prior to actual landfall. Amazingly, the verifying landfall location was only 30 mi south of the 5-day forecast! Thanks to improved model resolution, superior data assimilation techniques, improved model physics parameterizations, and utilization of ensemble methods, NHC is now able to predict points of landfall with unprecedented skill. Additionally, because of recent advances in ensemble forecasting, it is now also possible to better convey the uncertainty in the forecast than ever before. Ensemble forecasts can now reliably depict whether the uncertainty is in the cross-track or the along-track direction, and implementation of this information into the forecast is currently underway. These advances are only possible because of improved computing power and the unwavering ambition of hard-working meteorologists and computer scientists who devote their lives to improving the models and advancing the science. While we cannot always expect a 5-day forecast to go as well as it did for Sandy, track forecast errors continue to fall year-by-year in the Atlantic. This means better advance warning for the public and emergency management, more time to make preparations and protect property, and, most importantly, fewer lives lost.

Will Komaromi
Ph.D. Student
Meteorology & Physical Oceanography
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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

Hurricane Sandy Prepping for Frankenstorm Transformation

Latest visible satellite image of Hurricane Sandy, courtesy NOAA / NESDIS.

Hurricane Sandy has taken on the appearance of a mid-latitude nor’easter-type cyclone as seen from satellite. However, data from NOAA and Air Force reconnaissance aircraft confirm that Sandy is indeed still a hurricane with sustained winds of 75 mph and a central pressure of 951 mb. The latest forecast from the National Hurricane Center (NHC) keeps Sandy as a tropical cyclone for the next 36 hrs – through 8 pm (Eastern) Mon the 29th – before transitioning to an extratropical cyclone. However, as mentioned previously, this extra-tropical transition will not weaken the cyclone. Hurricane Sandy will become co-located with a region of favorable upper-level jet dynamics and baroclinic forcing, which will allow the cyclone to remain strong, if not intensify, right on through landfall. In layman’s terms, this means that a deep trough of low pressure over the Great Lakes region will re-energize Sandy. The global models did a very good job depicting the phasing between Sandy and the mid-latitude trough over a week in advance. Everything is on track for Sandy to become a “Perfect Storm” or “Frankenstorm” as previously predicted.

In terms of impacts, coastal NC all the way north into NY state are currently experiencing squally rainbands ahead of Sandy. Sustained winds of 49 mph with gusts to 63 mph have recently been reported as Cape Hatteras, NC. A tropical storm warning is currently in effect for much of coastal NC as well as Bermuda. These regions are either currently experiencing, or may experience during the next 48 hrs, winds sustained at tropical storm force (≥39 mph). While flooding has not been a major issue so far, rain has been persistent and slow-moving and is expected to worsen. Due to the abundance of rich tropical moisture, combined with the size of the system and slow movement, locations directly in the path of Sandy could see 5-10″ of rain, with up to 15″ locally.

Latest (11 am) forecast track for Hurricane Sandy. Image courtesy the NOAA National Hurricane Center.

Storm surge of 1-3 feet has been reported so far along the FL coast through GA, SC and NC, but should also get worse as Sandy grows larger and approaches the Mid-Atlantic coast. The current official NHC track forecast has Sandy making landfall anywhere from the MD/VA boarder through western Long Island on Mon night. While it is difficult to predict exactly how great the storm surge will be without knowing the exact strength, location, and angle of approach the storm will take, there is the potential for a 5-10 ft or greater storm surge in the hardest-hit areas to the right of where the storm makes landfall, anywhere from MD through Long Island or CT. Storm surge will be worst along SE to NW oriented coastal channels parallel to the wind field, as all the water is driven up-channel unimpeded, especially if landfall corresponds to astronomical high tide. Coupled oceanic models are also indicating that large waves of 10-15 ft will occur on top of this (and potentially even taller offshore).

Strong wind will also be a serious concern. Hurricane force winds will likely occur along the coast near and to the right of the landfall location. However, due to the very large size of the storm, tropical storm force winds will likely occur inland away from the coast. Power outages will likely be widespread, especially since trees blow over more easily in saturated grounds. Lastly, 1-2 feet of snow are likely to fall over parts of WV, with some lighter snow possible for western PA, western VA, and eastern OH. Please refer to your National Weather Service forecast office for official forecasts of local impacts and weather conditions. For evacuation and safety information, please refer to your local emergency management or law enforcement office.

Will Komaromi
Ph.D. Student
Meteorology & Physical Oceanography
Follow the Rosenstiel School on Twitter: @UMiamiRSMAS
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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

“Perfect Storm” Set to Occur on 21st Anniversary of Original Historic Event

Hurricane Sandy this afternoon, currently churning over the Bahamas and gradually moving northward. Image courtesy the NOAA National Environmental Satellite Data and Information Service (NESDIS).

The odds of a potentially historic meteorological event occurring in the vicinity of the northeastern United States next week are increasing. The players on the field are as follows: Hurricane Sandy traveling northward along the east coast of the U.S., a warmer-than-average Gulf Stream, a very deep upper-level trough over the central U.S. currently bringing snow to Colorado, and unusually strong high-latitude blocking (a very negative North Atlantic Oscillation / NAO). While Hurricane Sandy is currently bringing some rain, wind, and rip currents to South Florida, Sandy has the potential to bring even bigger problems to the Northeast. An increasing number of model forecasts are now “phasing” Sandy with the mid-latitude trough, and given the amount of upper-level jet energy available in this setup, this could become a particularly powerful phasing event.

Something similar happened in late October through early November 1991. It was known as “the Perfect Storm”, resulting in 13 fatalities and caused > $200 million in damages to the northeastern U.S. and fishing and shipping interests. In the Perfect Storm, northward-moving Hurricane Grace phased with a mid-latitude trough, similar to the one over the Central U.S. today. Normally a hurricane weakens as it moves northward, as it encounters an increasingly unfavorable environment. This means greater wind shear, drier air, and lower sea surface temperatures. However, with phasing events, the tropical system merges with the mid-latitude system in such a way that baroclinic instability (arising from sharp air temperature/density gradients) and extremely divergent air at the upper-levels more than compensates for a decreasingly favorable environment for tropical systems. The Perfect Storm deepened to 972 mb, and was at its strongest while out over the open ocean (but still whipping the coast with strong winds and heavy surf):

The co-location of an anomalously deep upper-level trough (left) directly over a strong surface cyclone (right) off the coast of the Northeastern United States during the Perfect Storm: Oct 30, 1991. Image courtesy of Pennsylvania State University meteorology department.

While there is still inherent uncertainty in the forecast, especially considering we are at least 5 days away from the phase, the majority of the numerical guidance has now come into agreement that a phasing event will occur precisely on the 21st anniversary of the Perfect Storm somewhere between the mid-Atlantic states through Maine or potentially the Nova Scotia region. Most of the models now indicate even stronger jet dynamics will occur next week than occurred during for the Perfect Storm, and that today’s storm could potentially deepen to well below 960 mb or even below 950 mb. The fact that the Gulf Stream is anomalously warm for this time of year means that Sandy will weaken less as a tropical system than it otherwise would have prior to the phase. Also, a very strong blocking scenario (very negative NAO) has developed over the north Atlantic means that the cyclone will be very slow moving, and is likely to retrograde westward into the northeastern U.S. rather than continue out to sea like most recurving extratropical cyclones do. While it is too early to pin-down exact impacts from the system at this time, it is likely that portions of the coastal Northeast will experience a damaging storm surge, significant beach erosion, and a prolonged severe wind and heavy rain event. Meanwhile, interior regions of western Pennsylvania into Ohio may simultaneously be experiencing heavy snowfall. Stay tuned!

The Global Forecast System (GFS) forecast for next Tue, Oct 30, 2012. Note that the cyclone is stronger and closer to the coast than during the Perfect Storm. Image courtesy of Pennsylvania State University meteorology department.

Will Komaromi
Ph.D. Student
Meteorology & Physical Oceanography
Follow the Rosenstiel School on Twitter: @UMiamiRSMAS
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