NY NJ PA Weather Forecasts

I’ve been working on all the 12Z model guidance this evening, while watching the Mets game of course.  Hey, I got to make sure they get to the play offs, right?

The main theme I’m going with for the end of the week is that the further south you are in the forecast area, the heavier and more likely you’ll see rain on Thursday through Saturday.  The main question on Thursday is just how much influence will the upper low off the New England coast will have on the Northeast and Mid Atlantic.  The models have been wavering on the influence of this upper low and the strong subsidence found on the back side of this upper low.  The stronger the subsidence, the stronger the dry air at the mid levels, and thus the limit on how far north the precipitation and warm front gets over the Mid Atlantic.  

I don’t like the timing of the GFS from Thursday through Saturday because the slow nature of the trough seen over the Great Lakes on the 12Z GFS is opposite of the actual progressive nature of the overall Pacific pattern that will begin to impact North America.  I think the ECMWF has a better handle on this pattern and the faster nature, which drives the warm front into the Mid Atlantic on Thursday and Friday followed by the cold front on Saturday.  

So therefore, my forecast from this morning still stands.  I am going with showers and thunderstorms on Friday with a more sustained, wide spread impact south of New York City.  A continuation of these conditions will be expected on Friday as the warm front slows the progression to the north over the southern Hudson Valley.  The threat for severe thunderstorms will increase south of New York City in the more unstable and warm atmosphere.  This is of course dependent on how far north the steady rain gets and how much break in the clouds can develop.  The cold front will move through the forecast area on Saturday and move through a very warm, humid, and unstable atmosphere.  Again, the threat for severe thunderstorms will return to the forecast area on Saturday afternoon.

The good news is that high pressure can be expected on Sunday and Monday with clear skies, low humidity, and comfortable temperatures.

By the way, the ECMWF also agrees with my thinking that Gustav will be an issue for the eastern Gulf of Mexico by the end of this Labor Day Weekend.

Well, it’s been a busy afternoon in the tropics!  While the remnants of Fay continue to spin over the Southeast, the impressive tropical disturbance over the eastern Caribbean Sea, rapidly developing into Tropical Storm Gustav this afternoon.  

Gustav this evening is a strong tropical storm.  A small pulsing down of the thunderstorms is being observed this evening, but given the favorable atmospheric conditions (no shear, no dry air, warm sea surface temperatures) I think we will see a continuation of intensification over the next 24 hours.  I firmly believe Gustav will become a category 1 hurricane before moving through western Haiti.  

The question is where will Gustav go after Wednesday?  The model guidance has little in the way of agreement on the track of Gustav after Wednesday.  Some models taking Gustav well south of Cuba to others moving Gustav over the Bahamas and everywhere in between.  

Lets take the model result out of the discussion for a second and look at what we have developing and what all the models agree with.  All the models agree that a ridge of high pressure will build over the Bahamas and over Florida at 850 MB to 500 MB.  All models agree that a trough will dig into the western Gulf of Mexico towards the end of the week.  This trough will be weak compared to the parent trough over the northern Plains, yet there should still be an influence strong enough to develop a southwesterly steering current.  As a result, I think what we’ll see is that as we move towards the end of the week, Cuba will be significantly impacted by Gustav.  Depending on how much land Gustav moves over, the circulation may be significantly disrupted.  However, once Gustav moves into the Gulf of Mexico, Gustav will have the potential to redevelop, intensify, and impact somewhere between Louisiana and the eastern Florida coast.  Where exactly, I’m not sure, but I think these locations will be under a threat by next weekend.

The tropical disturbance over the eastern Caribbean is looking very healthy this morning.  A low level circulation is clearly visible in the IR satellite pictures this morning with plenty of convection surrounding the center of circulation.  Cloud tops are becoming very cold, suggesting strong rising motion associated with this tropical system and favorable upper level conditions via anticyclonic circulation supporting outflow.  

I think this disturbance will become a tropical depression by the end of the day if not the end of this morning.  The circulation is becoming well developed and the upper level conditions will be favorable for development through the next 48 hours.

The future of this disturbance though should not impact the Gulf of Mexico.  An upper level low and the upper level winds from the eastern Gulf of Mexico through the western Caribbean will be from the southwest over the next seven days.  This will steer any tropical disturbance or wave that enters the Caribbean to move to the north over the Caribbean Islands of Cuba, Hispaniola, Jamaica, and Puerto Rico, which is exactly where I think and most models project this disturbance to go.  From there, the track of this disturbance is naturally unknown.  However, I would suggest any interest over the Bahamas or East coast should keep an eye on this system.

The local forecast discussion is updated.

A cold front will move through the forecast area today, but the dynamics are not very impressive to produce any significant severe weather.  In fact, the importance of this cold front is not what it does now, but what the cold front will become later over the Southeast.  The remnants of Fay are still causing havoc, and will impact the forecast area later in the week.  Just how much rain falls will still need to be worked out, but someone is likely to see over an inch of rain from the remnants of Fay by the time Friday is over.

Here are the themes covered in the technical forecast discussion.

1. Potential for severe weather is slim today.

2. Cool and comfortable conditions mid week.

3. Remnants of Fay to rain on some ones parade.