Will Sandy Be A Repeat of the 1991 'Perfect Storm'?

Many in the weather world are asking or being asked if Sandy will turn out to be a repeat of the 1991 Perfect Storm that brought chaos to the entire Northeast. Let's see what similarities they have.

SIMILARITY: Both events involve merging storms.
Both the 1991 Perfect Storm and Hurricane Sandy will/did involve the merging of storm systems. Sandy looks like it will merge with a system that is currently bringing cold air to the Midwest and Plains. This merging will bring Sandy inland.

DIFFERENCE: The number of merging storms is different.
Sandy will merge with one other system. The 1991 Perfect Storm managed to hoard two other systems for itself. In other words, Sandy will have less energy to deal with.

SIMILARITY: Both of these events will have tropical origins.
Sandy is currently a Category 2 hurricane, and will still be tropical before it merges with the other system. Hurricane Grace in 1991 was also a Category 2 hurricane in the northern Atlantic that eventually merged with two other systems.

DIFFERENCE: Hurricane Sandy has much lower pressure.
Hurricane Sandy has pressures as low as a major hurricane (Category 3+), while Grace was a short-lived hurricane. Sandy is stronger, Grace was technically weaker.

SIMILARITY: Both occurred in October.
As eerie as this is, yes, both Grace and Sandy are/were active in late October. What makes this story even eerier is how Sandy should make its landfall on the Northeast on October 30- the same day in 1991 that Grace was absorbed by another system, when the Perfect Storm technically began.

DIFFERENCE: Sandy originated in the Caribbean.
There's a major difference here. Hurricane Sandy originated in the heart of the Caribbean, home to moisture as abundant as water in the Pacific Ocean. Hurricane Grace began in the ocean to the far east of Florida, in waters not nearly as favorable as Sandy.

In short, Sandy and Grace were entirely different, and will end up entirely different. While both tropical and post-tropical systems have their similarities, there's a reason why it was named the Perfect Storm- because it almost never happens. Sandy will be a close rival to the Perfect Storm's make-up, but effects and overall composure of the two are pretty far apart.

Andrew

Hurricane Sandy Full Discussion (10/25/12)

Hurricane Sandy is currently a Category 2 hurricane that is located to the east of Florida at this hour. Satellite imagery indicates that Sandy is a very large storm with a very packed center. However, the southern flank of the system is fairly dry, and I would want to see more enhanced convection in that area to make sure the system sustains itself.

The National Hurricane Center, or NHC, has Sandy moving on a wobbly north track with an eventual curve to the northeast. However, as Sandy moves up the coast, a disturbance located in the eastern North America will drag the system in, causing the two to merge. Because of this merge, Sandy will be directed to the northwest and retrograde (storms moving west in the Northern Hemisphere) into the East Coast, making landfall as a post tropical system.

Models remain fairly confused with this system, although there is a general consensus for Sandy to move in the direction that the National Hurricane Center has Sandy going. There is potential for post-tropical cyclone Tony to grab Sandy and pull her out to sea, but I don't think this will happen and therefore prefer to side with the model guidance of a landfall on the East Coast. Due to the spread in the models when the system makes landfall, things are still a bit unsure as far as who could get snow and who could get the worst winds, but I have put out my best guess at the end of this post.

Rainfall will be a big concern with this system. The Hydrometeorological Prediction Center, or HPC, is indicating that many areas along the East Coast could get a healthy dose of several inches of rain. The heaviest rains look to be out to sea, where amounts in excess of 7 inches are possible as indicated on the above graphic.

The areas most at risk for snowfall include the Appalachians and part of the Ohio Valley, where the latest ECMWF and GFS have indicated the best chances for snowfall are centered. This risk of snow is moreso centered over the Appalachians, with the Ohio Valley thrown in there with more uncertainty than confidence. Because of the cold air being pulled south by Sandy, the lake effect snow machine should start going over the Michigan and Indiana sides of Lake Michigan. The Upper part of Michigan will also get in on some lake effect snow action.

Winds will be howling with Sandy. As she comes ashore, windy conditions can be expected across much of the Northeast, Ohio Valley and Mid Atlantic. The trouble begins in the Northeast, where some of the larger branches may break as Sandy roars in. Coastal cities in New York and Pennsylvania will suffer the worst winds, as offshore winds come on land and worsen the wind crisis. Entire trees will be threatened by these winds.

On The Weather Centre's Exclusive Impact Scale, I believe that only the Northeast and Mid Atlantic stand a chance at some enhanced impacts or major impacts on this scale, meaning property will be at risk and travel is likely to be disrupted. In areas immediately along shore, there will be 'Major Impacts', meaning significant travel disruptions and overall service disruptions are expected. Life and property will be at risk, mainly from winds and possible severe weather.

PERSONAL THOUGHTS

This storm will be a doozy. If I lived in the 'Major Impacts' area, I would want to stock up at the supermarket for supplies, as power is more than likely going to fail in at least some of the 'Enhanced Impacts' zone. Also, if you have any old or ailing trees in your neighborhood, keep an eye on them. Make sure your property is not in harms way, as trees of all ages may be damaged. Keep tabs on the elderly, those with disabilities, and those who, for some reason, need electricity in their lives (i.e. medical, for pets, etc.), as these people will be most prone to bearing the brunt of the storm's effects.

Andrew

Hurricane Sandy Staring Down East Coast

It should be noted that some information posted here is from yesterday's Sandy update. I repost it only because the information is still valid.

Tropical Storm Sandy has strengthened to a Category 1 hurricane as she moves a steady northbound track at this hour. Sandy has prompted hurricane warnings to be issued for much of the western Caribbean, with Florida also getting into the action. A tropical storm warning is in effect for the eastern coast of Florida, with a tropical storm watch surrounding that warning. With all the controversy swirling around Sandy, I still maintain my case that Sandy will pose a threat to the East Coast, and here's why:

The first thing we must examine is teleconnections. Above is a multi-model display of the 0z models and ensembles' predictions of the North Atlantic Oscillation. The North Atlantic Oscillation, or NAO, has two phases: positive and negative. In the negative phase, a colder and stormier pattern is encouraged over the East US as the jet stream dips south. In the positive phase, warm conditions can be found in the East.

Models are forecasting the NAO to stay well in negative territory, possibly well into November, but that's another story. The key piece is that the NAO will be extremely negative from now until October 27. Because teleconnections observations and their effects are delayed (the atmosphere doesn't work that fast), we want a good 3 day lag of negative NAO values before the storm strikes to show that the NAO would support such a possibility of an East Coast threat. Looking at the NAO forecasts, there is a good consensus on such a negative period through Halloween, which will enable the jet stream to dip in a negative NAO pattern. This provides a base for a theory on an East Coast threat.

Shown above are the ECMWF Ensembles on top and the GFS Ensembles on the bottom. Both are from today's 12z model suite. As you can see, both indicate that a strong system will hit the Mid Atlantic in the days leading up to Halloween. The two ensemble sets are pretty similar in forecasts- both have a strong storm crashing into the Mid Atlantic, and this situation would indeed pull down very cold air as the GFS ensembles depict on the lower image.

I believe that an ensemble set always triumphs over a single model. Why? Well, imagine the ECMWF model. It's a great model, very reliable, a very good model overall. Now imagine that same ECMWF model, but now there's 52 of them, combined into one overall forecast. It sounds too good to be true, almost like a sure-fire forecast (for the record, that's nearly impossible, no matter the model). That sums up what the ECMWF ensemble system is. The same goes for how the GFS Ensemble system works.


As the storm moves north (likely influenced by both the strong cyclone to the northeast and the advancing disturbance to the west), it has two options, which is the key player that is confusing the models. Here is a breakdown of each option.

Option 1: The storm moves north and is coaxed east by the strong disturbance located to the northeast in the image above. The storm keeps moving northeast and does not affect the US mainland.

Option 2: The storm moves north, but is more influenced by the disturbance in the Ohio Valley. The Fujiwhara Effect comes into play, and Sandy cycles to the west to orbit with the incoming disturbance over the Ohio Valley. This cycling persuades Sandy to move towards the US and make landfall. Personally, at this point in time, I am favoring Option 2.


I've run over the model forecasts and weather theories to give my first (but certainly not last) forecast on Sandy. Keep in mind that she will be EXTRATROPICAL (not a hurricane, but a strong coastal storm like the ones seen in winter). However, this does not mean that the tornado threat will be nil- such a post-tropical cyclone can definitely produce some tornadic activity.

DISCLAIMER: These are my own personal thoughts and are subject to major change in the next several days.
DO NOT use this information in place of official government weather information.

Andrew

Model Ensembles Prefer East Coast Landfall

Above, you see the GFS Ensembles on top and the ECMWF Ensembles on bottom, forecasting MSLP values in the Atlantic. They are both valid for 7 days from now.

The ECMWF Ensembles combine to believe that a strong system will make landfall in the Mid-Atlantic, with heavy winds and rain following along. I do not doubt the presence of some snow in the Ohio Valley from this system as well if the ensembles give enough cold air to the west of the original landfall.

The GFS Ensembles are even stronger and also hit the Northeast with Sandy at a strength in the 980's, indicating that the system looks to be pretty strong. It should be noted that for both sets of ensembles, some members are stronger than this, and some members are weaker than the forecasts above. This is a mean (average) of all of the ensembles within the GFS' base or the ECMWF's base.

I show you these forecasts because the models themselves may as well be as good as a life raft in the desert- sometimes it's practical (for shelter), sometimes it's not (there are no oceans in the desert). I think it's time to take a few steps back and see what the ensembles have to offer, because they are the best bet at this long range forecasting of a tropical cyclone.

Andrew

Long Range Lookout: ECMWF Late Fall-Early Winter 2012 Forecast

This is the ECMWF's Late Fall-Early Winter 2012 Forecast as interpreted by The Weather Centre. I will not provide the actual image out of copyright concerns.

The ECMWF's climate model is projecting a big swath of the Plains, Midwest and Rockies to be in a slightly cooler than normal state in this timeframe. No frigid temperature anomalies are expected to arise, although such a potential would be maximized in the Southwest states (New Mexico into Arizona). The Northeast and Southwest are portrayed as areas with above normal temperatures, the Northeast bearing the warmer brunt of the two.

As for precipitation, the ECMWF cites a below normal precipitation area across the meeting ground between the Northwest and Southwest. A chance of below normal precipitation is forecasted across parts of the Gulf Coast, but other than that, the ECMWF is relatively not concerned with the rest of the nation as far as precipitation anomalies go.

Keep in mind these forecasts are from one model of at least a few dozen- one fish in a never-ending sea, so to speak. So don't lose all hope just because one model says little precipitation is forecasted.

Andrew