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 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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“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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