Bryan Norcross' Official Blog

Great Forecasting and the Bottom Line

By: bnorcross, 4:17 AM GMT on October 31, 2012

When the tide was coming in Monday night, we were counting every inch of storm surge. There came a point when we knew, the hoping holiday was over... the water was going to win.

It was a confluence of every bad meteorological and astronomical thing you can imagine to create Sandy's catastrophic surge scenario, not to mention all of the other problems. The jet stream happened to kink into a most menacing and just perfect way that it could scoop up a hurricane that happened to be in the perfect position to be scooped. Then the combo mega storm just happened to move at just the right speed and track to pass over the Gulf Stream and then angle its winds for maximum storm surge, which just happened to come at high tide, which just happened to be on the night of the full, fall moon. Holy coincidence!

But in spite of that thread-the-needle-while-standing-on-your-head unlikeliness, last Thursday the National Hurricane Center put out their first forecast of a hurricane hitting the New Jersey coast... more than four days before it hit. On this blog, I had been talking about the possibility since the previous weekend.

Then when it came time to issue specific storm surge forecasts on Sunday - the NHC forecast a water rise at high tide of 6 to 11 feet at the Battery in New York - those numbers were perfect too. Nine feet was the final Sandy surge height.

But in spite of the forecasting side of the government house being on target, the communications side of the house was not thinking clearly.

I've been around a lot of scientists over the years, and I've found that they often don't think clearly about communications. Ask them for the bottom line and you get the top line, the middle line, and 10 reasons why you can't get to the bottom line. Bring a good communications person into the room and they get to the nub of the matter in 10 seconds.

The bottom line on Sandy is right there in the perfect forecast I mentioned above. The NHC forecast a real, live, tropical hurricane would be off the coast of Norfolk on Monday morning. The cone was covering the entire Northeast coast. A hurricane was coming and a Hurricane Watch should have been issued.

That's it. That's the bottom line. End of explanation.

NOAA said that the local National Weather Service alerts would be a better substitute. If I printed every locally issued watch, warning, or advisory that I get for just my house every year, I'd kill a redwood. Meanwhile we might, maybe, in a bad year get two Hurricane Watches or Warnings. They stand out. They get people's attention in a way that no local alert can.

How should the rules be adjusted to account for freak events like Sandy? That's for another day.

Today we offer hope and help to our friends who need it, and our thanks to the dedicated people who are working around the clock to restore what Sandy took away Monday night.

Hurricane Nor'Easter

Sandy... to Be Continued

By: bnorcross, 4:45 AM GMT on October 30, 2012

There's lots more to talk about with Sandy, but I'll save that until it's over. While the storm is winding down, there are vast areas along coastlines from Maryland to Delaware to New Jersey to New York to New England that didn't get news coverage... so we don't know what happened. When the sun comes up, we'll start to get an idea, though the morning high-tide cycle could still yield some local flooding, and winds are going to make it tough to get the power back on quickly.

The little bit of good news that developed late Monday, the dry air seriously overtook the circulation so the incredible rain amounts that the models were predicting are not going to be widespread. So it looks like the river and fresh-water flooding will not be as bad as predicted.

A little bit of good news is better than none... so I'll leave it at that for now.

Hurricane Nor'Easter

Sandy on Track and Serious Trouble

By: bnorcross, 2:59 AM GMT on October 29, 2012

And so it begins. Mega monster Sandy, with 40+ mph winds 900 miles across and embedded hurricane-force winds is going to hang a left and smash into the Northeast on Monday - a maneuver we've never seen before from system that originated in the tropics. There's no good news from the Hurricane Hunters or the computer forecast models. If anything, the storm is providing more drama in its first act than was expected.

Water is coming over sea walls. Flooding and whipping winds have already started. Just from the fringe of Sandy.

At the coast, by far the worst of this is going to come at high tide at the Jersey Shore and points north. The tide will peak along much of the Northeast coast around 9PM and 9AM, but around noon and midnight on the ocean side of Cape Cod. The difference between low and high tide can be 3 feet and more... a really big deal.

In a normal hurricane you can get lucky... the storm can come in at low tide, and then it's gone by the time high tide comes around. But in this case, the water will be high for a number of tide cycles, so there doesn't seem to be a way to avoid the full impact of the surging, smashing water and waves.

Waves of 10 to 20 feet on TOP of the storm surge and the tide are forecast for the south-facing beaches of Long Island. This will likely be the highest water and the most damage in many decades. On the north shore of Long Island and the south shores of Connecticut and Rhode Island, the water will be exceptionally high as well - likely exceeding Irene, which did major damage. Evacuations have been ordered. And water levels exceeding Irene are expected at many locations along the coast.

For folks staying home, if you're riding out the storm in a house surrounded by trees, stay on the opposite side of the house from the wind on a low floor. Close the curtains to cover windows facing the wind... but still be very careful near any glass that could break.

High rises in the big cities may be a problem. It's especially important that you stay away from the windows. If something flies off a neighboring building, it can smash windows downwind. Besides that, the wind is stronger because you're higher in the air, and the air gets squeezed between the tall buildings. The high wind stresses the glass, and makes it break more violently if something hits it.

It will likely take until Wednesday... or maybe longer than that... before we know what has happened. It's likely that transportation will still be difficult or impossible on Tuesday as the monster wind machine slowly spins down. Even Wednesday and Thursday we'll know that a giant storm is nearby.

That's it. Hunker down, be smart, and stay safe.

Hurricane Nor'Easter Winter Weather

Sandy on Track - But Is the Message Getting Out?

By: bnorcross, 3:44 AM GMT on October 28, 2012

Sandy the super-unusual, combo hurricane/nor'easter on the unheard-of track is coming together as forecast. The computer forecast models predicted that the winds would spread out in the nor'easter part of the storm, and the hurricane part of the storm would struggle a bit then recover. Tropical-storm force winds have spread out to the Virginia coast, and the tropical part of the system looks only so-so on the satellite.

Normally we would say the fat lady has sung, and get ready to fold up our hurricane hunters and go home. But, those same reliable computer models are saying that Combo Sandy is going to get reinvigorated by the jet stream while still getting energy from the Gulf Stream tomorrow and Monday, and get stronger and bigger. And then pounce on the Northeast.

The bigness of the circulation means big problems in at least two ways. A tremendous area from Canada to North Carolina to Ohio will be getting high winds from Sandy at the same time. That means trees down, power out, and a lot of miserable people in the chilly weather after the storm. And more importantly, the amount of energy the storm puts in the ocean water goes up dramatically with the diameter of the high-wind area. Not to mention, Sandy is already one of the biggest hurricanes on record.

When Sandy moves toward the coast, that high-energy water comes with it, which means high storm surge and stunningly high waves.

If the center of the circulation lands on the Jersey Shore, as looks most likely, the focus on that energy is going to be on North Jersey, New York Harbor, and the south shore of Long Island. The National Weather Service in New York is predicting waves 10 to 20 feet high on the south-facing beaches. Holy crap!

Did I also mention that's on top of the storm surge, which is forecast to raise the ocean level 4 to 8 feet above normal? And did I also mention that there's a full moon and the storm's peak is expected to be around high tide? Holy triple whammy!

That NJ/NYC/Long Island elbow is like a catchers mitt for storm surge, on the rare occasion that a big storm comes at it from the southeast or east... just like Sandy's forecast. The only thing that can stop extremely high water with battering waves from affecting the region is for the forecast to be wrong.

If the forecast is even mostly right, the ocean water will come in higher than during Hurricane Irene, which came within a foot of doing serious damage to NYC infrastructure. And that brings up the incomprehensibly inexplicable news conference by Mayor Bloomberg.

I'm NOT saying that the Mayor should have ordered an evacuation. That's for him to decide, and it's a tough decision. But to play down the biggest storm to come along in years - if the forecast is even close - seems bizarrely out of character. There's no upside in this everything-is-rosy approach. He could have expressed concern for the people whose houses are going to get smashed along the coast, but said AT THIS TIME he was going to hold off on any evacuation orders. A statement like that gives him room to maneuver and people get the message that preparation is required.

The normally well-oiled machine that is the Bloomberg administration seems to have slipped a communications cog.

And in a possibly related cog-slipping development, the National Weather Service decided NOT to issue a Hurricane Watch for the Northeast coastline... are you ready for this... because it would be confusing to switch from that to a Coastal Flood Watch and a High Wind Watch after the storm - which will come ashore with hurricane-force winds - morphs into another kind of storm according to the meteorology dictionary.

Whether the missing Hurricane Watch sent the Mayor off-kilter, we'll see. But the criticism came hot and heavy... enough that the Weather Service wrote up a big media release to explain why the clearest possible communications is a bad thing.

I grant that a technical reading of the "rules" says that you can't put up a Hurricane Watch and a Coastal Flood Watch and a High Wind Watch at the same time. But I'm betting the rules didn't envision a super-mega-combo freak of a storm slamming into the most populated part of the country. When all hell is breaking loose, sometimes you've got to break a few rules to do the right thing.

There will be a whole lot of talk about this when the storm is over. Hopefully that will result in a communication policy that meets the world-class standards of the forecasting that goes on at the Hurricane Center and at Weather Service offices all over the country.

The bottom line... let's all get on the same page. The forecast calls for a massive, destructive storm to affect tens of millions of people. If the forecast is wrong, hooray. But so far it's been right, and the odds are this is going to be really bad for a lot of people. Everybody's goal should be to be sure that as many people as possible are as ready and aware as they can be.

Hurricane Nor'Easter Winter Weather

Sandy: Serious As a Heart Attack

By: bnorcross, 4:05 AM GMT on October 27, 2012

It's one of the ugliest looking hurricanes you'll see, but Hurricane Hunters and satellite measurements confirm that its still tropical enough to be a hurricane... and its on track to cause a pile of trouble.

Two atmospheric processes are counteracting each other at the moment. Strong upper winds are trying to tear the storm apart, but a split in the upper flow is causing, essentially, a strong suction from above which is helping the storm keep going. This situation will likely result in some weakening... which would mean Sandy would drop below hurricane strength. But then the polar jet stream takes over and re-energizes the storm increasing the winds and growing the size. A sharp dip in the jet stream will pick up the reinvigorated Sandy and swing it toward the East Coast. At least that's the plan.

There are some ifs and maybes in that scenario, but the best computer forecast models independently insist that this is what's going to happen... and the not-so-reliable ones say the same thing. So, beginning immediately, it comes down to figuring out how to deal with it.

The ocean will rise along the coast as Sandy makes it's way north, but the biggest coastal problems will come when the center makes landfall. We're unlikely to know exactly where that will be until Monday, but this is critical. The ocean will be pushed toward the coast north of that point and away to the south. The onshore flow of water is exaggerated where bays, inlets, or the shape of the coastline focus the water to make it rise even higher. The most prominent problem spot is New York City, where Long Island and New Jersey make an "L".

Raritan Bay and New York Bay and the south end of Manhattan are especially susceptible to rising water if the center of Sandy comes ashore in New Jersey or south. Much as we saw in Irene, it is potentially a monstrous problem due to the threat to NYC infrastructure and transportation. There are tough decisions ahead for the Mayor and his people.

Right now, the odds favor that southern track. The threat from this situation is serious as a heart attack for anybody near the rising water.

Then there's the wind which is expected to be MUCH higher than Irene at the skyscraper level. The city will also have to be thinking about the threat to people in tall buildings.

The winds... expected to be at or near hurricane strength at landfall... will spread inland for hundreds of miles either side of the storm center. It's hard to imagine how millions of people are not going to be without power for an extended period of time.

Widespread rainfall of 3 to 7 inches with some places getting a foot or more will cause extremely dangerous flash flooding.

And then there's the snow. Heavy wet snow is forecast for the mountains of West Virginia and southwest Pennsylvania, mixed with rain at the lower elevations.

The winds will increase Sunday night in the Tidewater of Virginia and spread north through the day on Monday. The best guess right now is that the peak winds will come in overnight Monday night... near high tide and under a full, flooding moon. A triple whammy.

Let me think, what other disastrous thing might happen. It's storm overload, I know... and nobody likes to think about these kinds of things. Nothing here is certain, of course, just becoming more likely with every new piece of data. But one thing is for sure... if this all happens as forecast, and you and your family are stuck in the cold and dark without food and light and communications because you didn't run to the store and get ready... excuses are going to spectacularly hard to come by.

Hurricane Nor'Easter Winter Weather

The Sandy Paradox

By: bnorcross, 3:38 AM GMT on October 26, 2012

Isn't it strange that a hurricane in the Bahamas would somehow turn into a monster mega-storm and slam into the Northeast at the end of October? Aren't hurricanes supposed to weaken as they move north over cold water? What the hell is going on?

The answers are... yes, yes, and we're not completely sure. This is a beyond-strange situation. It's unprecedented and bizarre. Hurricanes almost always bend out to sea in October, although there have been some exceptions when storms went due north, but rarely. No October tropical systems in the record book have turned left into the northeast coast.

The strong evidence we have that a significant, maybe historic, storm is going to hit the east coast is that EVERY reliable computer forecast model now says it's going to happen. The only way we can forecast the weather four or five days days from now is with the aid of these super-complex computer programs run on supercomputers. The two best, the European and the U.S. GFS (Global Forecast System) run by NOAA, are now in reasonable agreement that there IS going to be an extraordinarily unusual confluence of events that results in a massive storm.

The upper-air steering pattern that is part of the puzzle is not all that unheard of. It happens when the atmosphere gets blocked over the Atlantic and the flow over the U.S. doubles back on itself. Sometimes big winter storms are involved.

The freak part is that a hurricane happens to be in the right place in the world to get sucked into this doubled-back channel of air and pulled inland from the coast.

And the double-freak part is that the upper level wind, instead of weakening the storm and simply absorbing the moisture - which would be annoying enough - is merging with the tropical system to create a monstrous hybrid vortex. A combination of a hurricane and a nor'easter.

At least that's what the models are saying. And since all of the independent models are saying something similar, we have to believe them and be ready.

For most people being ready means getting to the store and getting stuff before everybody else gets wise and gets the stuff first. The forecast is for an incredibly widespread and long-duration windstorm, meaning power will likely be out for an extended period of time in a lot of locations.

A transistor radio is your best friend in a situation like this. Get one and enough batteries to keep it going. Your cell phone may or may not be your friend after a big storm.

For people near the coast, it's critical that you pay attention to local evacuation orders and emergency information. This storm, as forecast, will create dangerous and potentially life-threatening storm surge along hundreds of miles of coastline north of where the center comes ashore. Big storms move a lot of water, and this one is about as big as they come.

Right now, it looks like the storm center will land between the Delmarva and New Jersey, which would put the entire Tri-State area of NJ, NY, and Connecticut on the bad side of the storm. The Jersey Shore, Long Island, and New York City itself would be exposed to the brunt of the storm surge due to the "L" in the coastline at NYC. The angle and duration of the wind will keep the water high for an extended period of time, if this comes together as forecast. This means transportation disruptions and widespread coastal damage.

If the storm comes in farther south, the Delmarva, Delaware Bay and maybe the Chesapeake will be at risk. A storm the size that's forecast would cause problems throughout New England as well, even if the center is south of New York. And then there is the threat from flooding rain and the extremely heavy snow well inland.

To make all this worse along the coast, the moon is full on Monday, meaning the high tides will be higher yet.

The hope we have is that the computer models are not handling this unusual situation well, and are predicting a stronger storm than we get. But, we can't bet of it. Even a weaker version will likely mean a nightmare for millions.

Hurricane Nor'Easter

Sandy Is Stronger... and the Forecast Is Complicated

By: bnorcross, 3:21 AM GMT on October 25, 2012

Sandy found a favorable patch of atmosphere and sea water between Jamaica and eastern Cuba... so a burst of rapid strengthening dropped the central pressure dramatically and the satellite presentation looks circular and impressive. But, Cuba's mountains are ahead and the atmospheric pattern is changing in complicated ways.

The Sierra Cristal and Sierra Maestra - mountain ranges in eastern Cuba - should disrupt the core of Sandy so a somewhat weakened version of the storm moves on toward the Bahamas on Thursday. And then the atmospheric situation changes dramatically.

Just to the west of Sandy there is a robust dip in the subtropical (southern branch) jet stream that is pulling down dry air. In fact, some of that dry air is already affecting the west and south side of the circulation.

As the storm moves through the Bahamas on Friday, the jet-stream dip will start to interact with Sandy. A number of things may happen simultaneously. First, the upper-level winds of the jet stream will create an unfavorable environment for the kind of strengthening we saw Wednesday night. Second, if or while the core of the upper winds are just west of the center of Sandy, they can have the effect of enhancing thunderstorms on that side - the Florida side - of the storm meaning stronger winds and heavier rain at the coast. Third, the energy from the jet-stream can begin the transition of Sandy to a hybrid type of storm with a large center and strong winds spread out over a much larger area.

These large-diameter storms, whether they are tropical like Ike or Irene, or nor'easters like a big northeast blizzard, produce storm surge and other effects a long way from the center. In fact, the weather near the center is often not significant at all.

As a result, threatening storm surge is expected on many of the populated islands in the Bahamas. In Florida, extremely high seas will cause major erosion on the east-coast beaches, and some strong wind gusts may effect coastal sections, depending on how and where those west-side thunderstorms develop. More than local flooding from rainfall is not expected.

Then it really gets complicated. The jet-stream dip over Florida is expected to push Sandy north of the Bahamas on Friday and perhaps nudge it a bit to the west... as the high winds spread out from the center. The highest winds will likely be at or just below hurricane strength, but over a larger and larger area. It looks like Sandy will ride the Gulf Stream a long way north, so it should be able to maintain its strength as it passes the Carolinas with similar effects to Florida, but a longer duration of wind.

The most logical forecast is looking more and more like a direct hit on some part of the coast between the Delmarva and Maine. The American GFS computer model wants to turn the storm out to sea and then loop it back to Canada, but it seems to be heading directly into a strong, blocking high pressure system, which doesn't look likely. Most of the rest of the credible models, including the multi-run ensembles, bring the system directly to the coast.

The effects of the storm are likely to be widespread - many hundreds of miles - but there are still a lot of variables. How strong will it be? Maybe the upper-level winds over the Bahamas wound it so it can't recover. Does the southern jet-stream dip push it farther east, which changes the track father north? Where does the center make landfall, if it does? The biggest coastal threat, by far, will be north of that point. If landfall misses your location to the north, coastal impacts for you would be dramatically reduced, though you could still have a long duration of strong winds.

The key take-away is the same as it has been. The consensus of the best computer forecasts we have is an extremely strong storm on an unprecedented track into the Northeast or New England on Monday or Tuesday, depending on how far north it tracks before turning inland. We'll know more by Friday when we see how the interaction with the jet stream comes out and where it is at that time. But, for now, everybody along the East Coast needs to stay informed and be ready to get prepared for an extended period without power and all of the other problems cause by a hurricane-like storm.

Hurricane Nor'Easter

Threat of Northeast Effects from Sandy

By: bnorcross, 2:00 AM GMT on October 24, 2012

Wow... what an extraordinarily unusual scenario. What seemed like a fluke of an idea - a hurricane-like system hitting the northeastern U.S. - is gaining credibility. Originally the European model was on its own with the spectacular but somewhat bizarre idea that Sandy would be injected with jet stream energy and curve back toward New England as a stunningly strong storm. Now one model after the other, including the ensembles, are favoring a swing back toward the East Coast after the storm goes by Cape Hatteras.

This the the afternoon run of the American GFS model ensembles - multiple lower-resolution runs with slightly different initial information, which allows for the fact that we can't measure the atmosphere precisely among other things.

The majority of the possible tracks now head into the Northeast, New England, or Atlantic Canada.

Could it really be a strong hurricane, as the European model predicts? We know that, occasionally, hurricanes do occur at these high latitudes at the end of October. Famously, the "Perfect Storm", otherwise known as the Halloween Hurricane battered New England in 1991. Also, Category 2 Hurricane Ginny hit Nova Scotia in late October 1963. But, neither were of a scale and impact like the Euro is showing.

With the influence of the jet stream, you would think any storm that comes ashore would be subtropical in nature - part tropical and part like a nor'easter - but the NHC doesn't allow for subtropical hurricanes in their naming scheme. It's considered to be such a rare and nearly impossible event.

The spectacularly unusual confluence of events is the shape and orientation of the dip in the jet stream that is forecast to develop over eastern North America over the weekend - oriented in such a way to pull Sandy inland instead of pushing it out to sea, and the presence of a strong tropical or subtropical system where it can get pulled in. That's so bizarrely unusual that I can't think of another event like it.

This kind of thing occasionally happens with nor'easters, notably the Great Appalachian Storm of November 1950 which curved in off the Atlantic and dumped 20 to 30 inches of snow over a wide area in the Mid-Atlantic and Midwest, but the odds of it happening with a system that originated in the tropics - with all of the moisture that that implies - are extremely low.

We certainly don't know that it's going to happen, and our concern at the moment is for our friends in the Caribbean and the Bahamas who will take a direct hit from a strengthening hurricane. The Florida and Carolina coasts also need to be ready to take protective action - especially boaters and people right at the coast - depending on the track Thursday to Saturday. But it's not often that credible forecast models consistently forecast a historic event, and with more models leaning that way, we need to be aware and pay attention along the entire U.S. East Coast.

Hurricane Nor'Easter Winter Weather

Sandy and the Fork in the Road

By: bnorcross, 12:13 PM GMT on October 23, 2012

The forecast dilemma for Sandy continues as we look ahead to the weekend and beyond. For the next few days, the center of the strengthening tropical storm and likely hurricane will move north out of the Caribbean with direct, life-threatening impacts on Jamaica, eastern Cuba, Haiti, and the Dominican Republic tomorrow into Thursday. These islands all need to move to an alert status.

It also appears likely that much of the Bahamas will get flooding and high winds Friday into Saturday, similar to Hurricane Noel in 2007, with Florida feeling fringe effects, especially along the east coast.

Then things get murky, with the two groups of computer forecast models heading in different directions... two forks in the road. Both the American GFS and the European ECMWF show the jet stream dipping down from the north and beginning to affect the storm. The GFS affects it in the traditional sense of pushing it out to sea.

The European develops a jet-stream dip of VERY unusual shape and intensity, however, which wants to grab Sandy, inject significant energy into the system, and pull it north as a MEGA nor'easter.

This is an extremely unusual pattern which yields an extreme result, but it can't be totally discounted as a possibility. The European model has been the most accurate computer model for the last few years, though it has had some spectacular misses as well.

The upper-air disturbance that is forecast to turn into the jet-stream dip that grabs or doesn't grab Sandy is still developing off of western Canada... and there are a lot of pieces to fall into place. So for now our concern is for our friends in the northern Caribbean, but we watch for developments as the northern pattern develops over the next few days.

The fork comes around Saturday, so everybody from the Mid-Atlantic to the Northeast and well inland will need to pay close attention to developments.

Winter Weather Hurricane Nor'Easter

When South Meets North - The Evolving Scenarios

By: bnorcross, 12:14 PM GMT on October 22, 2012

The tropical disturbance in the Caribbean is getting better organized... and is close to tropical depression status. The upper-air pattern is conducive for it to develop into a tropical storm and perhaps even a Cat 1 hurricane this week. It will likely be "Sandy", though there is a disturbance some 700 miles northeast of the Leewards that has a slight chance of beating it out. The next name would be "Tony".

The best computer forecast models - the American (GFS) and the European (ECMWF) - tell the same story for the next few days... the tropical storm brings extremely heavy rainfall to the northern Caribbean islands midweek. The strengthening storm - either a strong tropical storm or a hurricane - then moves through the Bahamas Wednesday through Friday.

The main effect in the U.S. in this scenario is an extended stretch of windy weather along the Florida east coast causing high surf, beach erosion, and some high-tide flooding.

Beyond that, the models are telling a different story. The GFS takes the tropical system out to sea, like tropical systems are supposed to do in October, and a strong kink in the northern jet stream spins up an separate nor'easter-like system off Long Island a week from now.

The European mixes the tropical system with the northern jet-stream energy and creates a mega winter storm across parts of the northeast back to the Great Lakes.

It's a crazy pattern, but these very sharp kinks in the jet stream caused when a big blocking high develops in the Atlantic are how oddball scenarios develop. For now we stay tuned. No doubt it will change again a number of times. Our main immediate focus is on the Caribbean and the potential for life-threatening rainfall across the northern islands.

Hurricane Nor'Easter Winter Weather

A Tropical System Meets the Changing Season

By: bnorcross, 8:50 PM GMT on October 21, 2012

The most accurate computer forecast models are in amazing agreement today, and if they are right, a system will move out of the Caribbean this week having significant effects on the northern Caribbean islands, the Bahamas, and perhaps the East Coast of the U.S. The scenario is complicated involving both tropical and wintertime atmospheric features - but it's not impossible.

In some ways this is reminiscent of Hurricane Noel in 2007 which caused devastating flooding in Cuba, Haiti, the Dominican Republic, and the Bahamas. In addition, several days of strong onshore wind caused millions of dollars of beach erosion along Florida's east coast, with strong winds in New England and Atlantic Canada as well. The peak winds during the multi-day onslaught were sustained at 43 mph with gusts to 54 mph in Miami Beach. On Nantucket the winds gusted to 72 mph and in Newfoundland they recorded gusts of 112 mph.

An organized low pressure system hasn't even formed yet in the Caribbean, so a LOT can happen, but because the scenario is so dramatic, it's going to require our attention.

In a nutshell, the models show a strengthening tropical system bringing flooding rains to the Caribbean islands and the Bahamas. Then the northern jet stream grabs it, injects some energy, and the storm moves north along the U.S. east coast and evolves into a VERY strong Nor'easter... all the way up to Atlantic Canada. Nor'easters wrapped with tropical moisture can be nasty because you get the contrast of extremely moist southern air and cold northern air in the same circulation.

Along the east coast of Florida, if anything like this scenario plays out, the combination of the tropical low pressure in the Caribbean and the high pressure to the north will bring increasing onshore winds all week, becoming very windy by late in the week. The worst of the rain would stay offshore, but significant erosion and flooding at high tide would seem likely.

Farther north, the forecast models show a monster nor'easter affecting the entire East Coast of the U.S. through next weekend, with coastal rain and wind and likely snow inland, but a small difference in track would make so much difference in the effects a week from now, it's just something to watch at this point.

You might say, "this all seems pretty implausible", and I can't remember one exactly like this. But, recall that last winter we were stuck in a pattern that resulted in spectacularly warm weather in the north because of a "blocking" high pressure system in the North Atlantic. Well, the models are developing a big blocking high again next weekend, and that forces the system on a more northerly track than normal... along the coast. Most storms in October head northeast out to sea.

The bottom line, unusual/extreme weather patterns often yield unusual/extreme weather. This is pretty unusual, so it bears watching closely. Stay tuned.

Hurricane Nor'Easter

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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About bnorcross

This is the official blog for Bryan Norcross, Hurricane Specialist at The Weather Channel.

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