New York City Metro Weather

Hurricane Irene to pound the NYC metro area; warnings in effect

By: NYCvort, 5:24 AM GMT on August 27, 2011

***A HURRICANE WARNING IS IN EFFECT FOR THE NYC METRO AREA***




SAT 8/27 11 AM UPDATE

As of 11 am, Irene is currently a category 1 hurricane with maximum sustained winds of 85 mph. New model data continues to support the a track that will take the center of the storm somewhere between the Jersey Shore and western Long Island.


Much like a seesaw or balance, energy coming down from the upper midwest will send Irene back into the coast, rather than a more usual recurving track.

This is an extremely rare occurrence.

If a mandatory evacuation has been issued for your area, please be sure to evacuate. Do not attempt to ride out the storm. With the storm tracking so far to the west, one of the most dangerous aspects of this hurricane will be the storm surge near the shore. This is why evacuations of susceptible areas have been ordered, and they must be followed so as to not put you and your family's lives at risk.

In the remainder of the area, prepare for strong damaging winds and a prolonged period of very heavy rainfall.


Like I said yesterday, there will also be the potential for isolated tornadoes. Please keep in tune to the latest watches and warnings via radio, TV, or by visiting the National Weather Service at http://www.weather.gov/okx/.


Current Water Vapor Satellite (automatically updating image):




FRI NIGHT UPDATE

My main concern regarding the track of this hurricane is that I was having a hard time finding something that would drive the storm into the coast. A meteorologist on the AmericanWx forums highlighted a small piece of energy located over the upper midwest that was being handled differently by the ECMWF and GFS models. It appears the ECMWF model has been using that small disturbance to essentially pull on Irene and keep the hurricane on a coastal hugging track. I’ve been keeping a close eye on that disturbance the last few runs, and sure enough, the GFS appears to have caught on. I highlighted this small piece of energy that is now featured on tonight’s GFS run:


More than likely it is the fact that the ECMWF model has a higher resolution than the GFS and was able to see it when the GFS could not because of its lower resolution. Consequently, the GFS has now shifted Irene’s track westward.

At this point, I now feel confident on a more western solution panning out. The GFS is the farthest east and this may be because it is still not capturing the strength of that piece of energy completely right just yet. So, I’m leaning towards a track that would take the center of the storm somewhere between the Jersey Shore and western Long Island (generally along the lines of the 0z/27 NAM). Such a track would put Long Island into the front right quadrant of the storm and lead to significant storm surge potential near the shore. Isolated tornadoes cannot be ruled out. Highest rain totals will be on the western side of the storm, likely over New Jersey and west of the Hudson. Amounts could surpass 10 inches in some spots, with upwards of 7 inches across most of the area. As such, a flood watch has been issued.

This track of the storm will allow for some weakening. Irene is forecast to be a category 1 hurricane at arrival. This will bring very strong damaging winds into the area.

More updates tomorrow.



Opinions expressed in this blog are my own and should not be used to make decisions. For official forecasts on Hurricane Irene, please visit the National Hurricane Center at http://www.nhc.noaa.gov/.tumblr page counter

Hurricane

Updated: 3:40 PM GMT on August 27, 2011

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An earthquake and a hurricane threat all in one week?

By: NYCvort, 9:53 PM GMT on August 23, 2011



A HURRICANE WARNING HAS BEEN ISSUED FOR THE AREA


FRI 9 AM UPDATE

The National Hurricane Center has issued a hurricane watch for the New York City metro area. A hurricane warning is now in effect for the New Jersey coast on southward.

Irene is currently a category 2 hurricane. The NHC believes that some re-intensification is possible during the day today. They have adjusted their track slightly eastward from last night, and it is gradually coming more in line with my thinking.

I will update again later today after the 12z model suite. The last piece of the puzzle has now come ashore per the water vapor, so we should have an even better idea of the exact track by this evening.

Current Model Spread (automatically updating image):


Current Water Vapor Satellite (automatically updating image):




THU NIGHT UPDATE

A hurricane watch has been issued for areas in the mid-Atlantic from coastal New Jersey on southward.

Over the past day the models as a whole have trended significantly westward in track. Such a track would put areas near the shore of the city and coast at high storm surge risk in addition to heavy rain and strong damaging winds. My own feeling is still that this storm will track slightly farther to the east, with a landfall near eastern Long Island. Such a track would bring a prolonged period of very heavy flooding rains along with strong winds; however, storm surge concerns along the south and east facing shores would be diminished somewhat for NYC, NJ, western LI, and southwest CT.

Regardless of the exact track, preparations should be made now in advance of this storm. If you live near the shore, pay attention to evacuations.

More updates to follow.



WED 8/24 5 PM UPDATE

Just to update the 12z Euro is a western outlier showing the hurricane making landfall on the New Jersey coast. This is the latest ECMWF for Sunday:


The GFS/GGEM are both middle of the road solutions taking the storm just slightly east of my projected track I discussed yesterday. This is the latest GFS for Sunday:


Each of these scenarios would come along with its own set of problems. The Euro solution would not bring nearly as much rain, but it would still be windy and coastal flooding would be significantly worse with strong storm surge. There would also be the potential for isolated tornadoes. The GFS solution would bring a prolonged period of very heavy rainfall along with strong damaging winds.

The GFS ensembles along with a few of the hurricane models continue to take Irene well off to the east with significantly less impact all around. I still like my original track. This would be more along the lines of the GFS solution. However, the models are still handling both the amplitude and timing of this weekend’s trough erratically and also how Irene actually interacts with that trough. For that reason, the exact track of Irene still remains very much uncertain.

The reason why the GFS today has backed off a bit on the eastward trend is largely because it has been projecting that trough over southeastern Canada this weekend to be less amplified:


Rather than a strong trough forcing Irene out, the weaker trough would have less impact on Irene, so the GFS nudges the hurricane slightly closer to the coast. The trough on the European model looks very similar but it’s just slightly slower and oriented a little differently, which ultimately results in a drastically different scenario as seen above. We still need to wait for better consistency on that all-important trough.

Just a quick look in terms of intensity, most of the hurricane models keep Irene as either a category 1 or category 2 hurricane during its projected time of nearest approach (red shaded region):


More updates on the way tomorrow, so be sure to check back.



ORIGINAL DISCUSSION

Now that NYC has dealt with the surprising scare of the aftershocks of a 5.9 magnitude earthquake, a hurricane will threaten the city and coast late this weekend.

Once tropical systems become strong enough, the warm core cyclonic circulation extends straight up into the high levels of the atmosphere. This means that they are steered by the features that can be observed at the 500mb level. For this reason, Hurricane Irene’s path will be very much dependent on what is going on across the eastern US. On her long voyage across the Atlantic, as a weaker storm, Irene was steered by the easterlies located on the southern periphery of high pressure positioned in the central north Atlantic. Even as she strengthened considerably the last few days, the Atlantic ridge extends into the upper levels of the atmosphere so a westerly track pursued. Hurricane Irene has begun to shift ever so slightly toward the WNW during the last couple days with increasing influence from a weakness that has developed as a result of the trough that has brought us this nice cool start to the week.



This trough is currently lifting out, but a weakness (or break) in the high has formed near and just off the southeast coast. The doors have been open and now Irene will gradually lock into a northwest path as weak shortwave ridging builds over the eastern seaboard tonight. Another trough will begin dropping into the Great Lakes region by late tomorrow. A piece of Pacific energy will phase with the trough and then that trough will dig into the Ohio Valley and northeast on Thursday.



This is where things get more interesting. The models have been both making this trough more amplified and also slowing down its passage. In addition, I’ve noticed that the models are trending towards a more positively tilted trough. I have done my best to illustrate this by showing the recent runs of the GFS and NAM below:





This allows for more “pull” on the storm and for a longer period of time. Since the trough is more positive, Irene is directed farther to the east rather than being sucked in toward the coast. As a result, the increased southwesterly flow on the southeastern edge of the trough will cause Irene to turn rather abruptly toward the north late in the week, rather than continuing on a more westward track. Shortwave ridging looks to build in briefly once again late Friday with Irene continuing toward the north.

Another trough swings across Canada this weekend. Some of the operational models were and the ensembles continue showing that second trough being a bit stronger and thus causing Irene to curve toward the northeast. Now the operational models have weakened this trough and caused it to continue on its northward track. This is the most dangerous path for the mid-Atlantic and could bring Hurricane Irene’s direct effects into our area. All of the 12z model runs show the possibility of a near direct hit from Irene on Sunday.

GFS:


ECMWF:


Canadian:


Each of these runs taken verbatim would bring copious amounts of rain and damaging winds to the entire area, as well as storm surge/significant flooding near the shore. However, the important thing to remember is that we are still several days out at this point and many of the ensembles show a completely different story, with both troughs more amplified and thus a solution that takes Irene on a close call path for us, similar to Earl last year.

To give a sense of how many possibilities are still open, here are the current tracks from the dynamical hurricane models:


And here are the individual GFS ensemble members:


Note how the dynamic model tracks tend to cluster around the operational guidance while the ensembles remain more of an outlier on far right. I wouldn’t completely rule out a passage to the east. We do continue to see an amplified pattern (perhaps a result of the changes going on the tropical Pacific that I highlighted last week), with a positive PNA forecasted and weak negative NAO to block things up a bit.


Here is a visual illustration of how the two troughs significantly influence the track. For each I used a comparison between the GFS operational and one of the farthest east ensemble members.

First Trough:


Second Trough:


Note how the ensemble member amplifies both troughs to a greater extent, and, as a result, takes Irene from a fairly close proximity as the operational model in the first image, to a position well to the east in the second image. The NHC is currently forecasting a track near the mid-Atlantic coast. My personal opinion is that this track may be slightly too far west.


The potential threat from Irene is real. If I had to pick a track, I would probably stay a bit east of the NHC track with the center of the storm just off the outer banks of North Carolina and then across far eastern LI and into southeastern New England, similar to the GFS. That’s my best guess at this point. I would say there’s a better chance of this storm going east rather than west. We will need to continue to keep a very close eye on the projected track of Hurricane Irene over the next several days. I will try to provide updates in the comments section or at the top of the blog entry, so be sure to check back.

-NYCvorttumblr page counter


Opinions expressed in this blog are my own and should not be used to make decisions. For official forecasts on Hurricane Irene, please visit the National Hurricane Center at http://www.nhc.noaa.gov/.

Hurricane

Updated: 8:54 PM GMT on August 26, 2011

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Examining effects of upper wind anomaly changes in the tropical Pacific

By: NYCvort, 8:30 PM GMT on August 17, 2011



In my last discussion I highlighted the idea that the semi-permanent ridge located north of Hawaii for most of the summer would retrograde and lead to some big changes. So far we’ve seen a cooler and much wetter pattern. However, it is interesting to note that we are already seeing a ridge build back north of Hawaii with some warmer weather expected the next several days. But I still think we will see a gradual return to a cooler and wetter pattern once again during the next couple of weeks. The force that will drive this change in pattern may already be in motion over the eastern tropical Pacific.

For the past 10 months, 200mb zonal wind anomalies in the tropical Pacific have averaged greater than 1 standard deviation above normal:

This can be attributed to the strong La Nina and its associated effects on the atmosphere since last fall. However, we have recently seen the La Nina fade away and ENSO-neutral conditions develop this summer. For the past several days, the GFS and ensemble mean 14 day forecasts have been indicating that the 200mb mean zonal wind index in the tropical Pacific will drop to between 1 and 2 standard deviations below normal:


Should this pan out as forecast, the pattern of upper wind anomalies would likely change as a result over much of the northern hemisphere, with a stronger southern jet stream and weaker northern stream. Composites of past 200mb zonal wind patterns during the month of August can help to illustrate what can be expected with such a change. I inserted arrows to more easily discern anomalous wind direction.

Upper level wind pattern with positive (westerly) 200mb zonal wind anomalies in the tropical Pacific:

Note with westerly anomalies over the tropical Pacific, we see easterly anomalies develop over the north Pacific into the US (indicative of weak southern jet stream) and corresponding westerly anomalies over the Gulf of Alaska into Canada (stronger northern stream). This is what we have been experiencing.

Now here is how the 200mb winds would change.

Upper level wind pattern with negative (easterly) 200mb zonal wind anomalies in the tropical Pacific:

Note with easterly anomalies over the tropical Pacific, we see westerly anomalies develop over the north Pacific into the US (indicative of strong southern jet stream) and corresponding easterly anomalies over the Gulf of Alaska into Canada (weaker northern stream).

I also created 500mb geopotential height composites to graphically illustrate the upper level pattern that results out of these zonal wind anomalies.

500mb pattern with positive (westerly) 200mb zonal wind anomalies in the tropical Pacific during the month of August:

Note the ridge north of Hawaii, just as we have seen it as of late. Some of the other features look very roughly similar as well to what we have seen much of this summer.

Now here is how the 500mb height pattern would change.

500mb pattern with negative (easterly) 200mb zonal wind anomalies in the tropical Pacific during August (top) and September (bottom):


Note how we see an opposite pattern develop north of Hawaii, with a negative anomaly (or mean trough) in the same position. Both composites show some degree of ridging over western North America downstream of the trough, with negative anomalies in both images over the midwest and into the east. A September pattern like the one shown would almost certainly lead to above average precipitation, as we would be positioned on the eastern side of a mean trough and there would also be a stronger subtropical jet stream (as noted earlier in the wind pattern composite). Not to mention the fact that this pattern would leave the door wide open for moisture from tropical disturbances. In fact, composites of those same years during the month of September do show near normal temperatures along with above normal precipitation along the east coast:


It is interesting to note that the 8-10 day mean 500mb height patterns on both the ECMWF and GFS look quite similar to the September composite above (although our pattern continues to show significantly more high latitude blocking than the composite).

Note the trough north of Hawaii, ridge over western North America, and trough in the east.

The GFS ensemble mean is indicating the return to a neutral PNA by the end of the forecast period. However, should these changes in the upper level pattern over the tropical Pacific result, we would likely be following the high end of the ensemble PNA cluster, with a positive PNA index prevailing.


As the pattern begins to shift, we’ll see a cool air mass dump in early next week. After that, we will need to consider how long the negative/easterly 200mb wind anomalies in the tropical Pacific remain in place and how strong they become. Regardless, this suggests a change to a cooler (in relation to the well above normal temperatures we’ve been experiencing) and damp pattern to end off summer.

-NYCvorttumblr page counter

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Cooler weather pattern taking hold in the extended

By: NYCvort, 10:34 PM GMT on August 08, 2011



This morning’s observed 500mb pattern:

In this morning’s 500mb analysis we see three separate disturbances that will all contribute to the development of a negatively tilted trough late this week, which will extend from southeastern Canada into the northeastern US.

Pattern by late week:


So let’s begin with today. The piece of energy currently moving across southern Canada will phase with the polar vortex over Hudson Bay. This will cause a surface low pressure system over Canada to deepen. In the meantime, front running energy in the Pacific jet stream will allow for a secondary area of low pressure to develop in our vicinity Tuesday night. This will lead to a widespread area of showers and thunderstorms developing Tuesday afternoon and continuing overnight.


The low will be slow to exit on Wednesday and with not much of any cold advection directly behind it, temperatures will manage to make it will into the 80s but it will begin to feel more comfortable with slightly lower dewpoints. The aforementioned elongated trough will swing through Wednesday night, with 850mb temperatures dropping to around 10°C. In addition, high pressure will begin to build in from the west Wednesday night with dewpoints falling into the 50s as northwesterly flow develops into Thursday.

This dry and cooler air mass will result in comfortable weather for the latter part of the week, with highs in the upper 70s to low 80s. It will also be good sleeping weather with nighttime lows in the 60s area-wide, with even some 50s in the outlying areas. Overall, temperatures will be near to just slightly below average.

Oftentimes when a negatively tilted trough lifts out, a ridge builds in rather quickly and temperatures rebound with significantly warmer weather to follow. However, the good news (assuming you don’t like the heat) is that this will not be the case here. As the surface high drifts offshore, we will see flat shortwave ridging build in aloft very briefly on Saturday, but additional energy will already be moving over the Great Lakes.

This energy will slide into our region on Sunday, and, as a result, a cold front will approach with a round of heavy showers and thunderstorms, followed by more pleasant weather early next week.

The main question is what has changed. So far this summer we have seen temperatures running about 1.5°C, or 2.7°F above normal.

This can be at least partially be attributed to a semi-permanent ridge located north of Hawaii. Downstream, this has resulted in a mean trough position over the west coast and a ridge centered over the upper midwest. With plenty of blocking over the high latitudes, a weakness was often present over the far western Atlantic between the midwest ridge and Greenland ridge.

This summer’s mean 500mb pattern so far:

Energy continued to come around the ridge north of Hawaii, dumped into the western US trough, and helped to pump up the ridge over the midwest. We remained in a prime location for warm temperatures in the mid levels of the atmosphere to come up over the ridge and spread into our area. A ridge axis in this position also allowed for the mean surface high position to be to our southwest, with an offshore, downsloping flow much of the time and little ocean influence at the surface. This general pattern was remarkably similar to last summer’s but with less amplification and less warm air to work with (thus shallower ridging) in general following last winter’s La Nina.

A more amplified pattern will be developing over the Pacific during the next week, with the ridge north of Hawaii retrograding and a big trough setting up over the Gulf of Alaska. This trough will keep the ridge in a position near the Aleutian Islands and prevent it from building back eastward for a time.


As a ridge sets up over western North America downstream of the big GOA trough, this will likely cause the PNA index to stay positive for the next week or two, with some of the highest PNA index values expected since May.


This will lead to a mean trough in the east, which is the reason why (as discussed earlier) we will see additional energy moving in this weekend before a ridge has a chance to build. Another thing to keep in mind is that the NAO is in a strong negative state, and even though it is forecast to rise significantly over the next week with the positive anomaly near Greenland weakening a bit, a big part of this is that the anomalies are changing position. Not only will the AO still remain negative, but a look at the extended GEFS also shows plenty of high latitude blocking and a weak west-based negative NAO continuing with good chances for a ridge axis just to the west of Greenland.

West-based negative NAO continues:


AO remains negative:


This is an ideal pattern for a mean trough to remain over southeastern Canada, and even into the northeast assuming what’s happening upstream over the Pacific continues to favor it.

-NYCvorttumblr page counter

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About NYCvort

I am a meteorologist from New York who has been studying and forecasting the local weather for years. I especially enjoy tracking winter storms.

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