The subject title is my attempt at singing Maria from West Side Story. . .it sounds better up there. Anyway, Maria is all that is left of this latest burst of tropical activity. She has had a very hard time maintaining. . .wait, how about surviving in a very hostile Atlantic pattern. An upper-low has been playing with her emotions and ripping away any thunderstorms that try to develop near the center. This leaves us with a strung-out, disorganized (sound familiar this season?) tropical storm that will quickly fade north-northeast in the next few days. The only threat may be some tropical storm force gusts of wind near Bermuda, then maybe some flirting with New Foundland.
The above animation (click on the image to animate if it isn’t already) shows yet another tropical storm that looks like half a storm. I mean, the sun is shining to the west-northwest of the surface circulation.
The culprit to the shear is a ghost of its former self. The red “L” denotes the approximate location of the surface low that is Maria. The black dashed line is a remnant trough around 500 mb (12000 ft) of what was once an upper-level closed low. The shearing is still there, but the upper-low has opened up into this trough or weakness. Finally, the blue line is the next trough which has started to exert some influence on Maria. The broad southwesterly flow ahead of the trough is turning Maria north-northwest and will guide her safely away from the U.S. The storm should stay west of Bermuda, but the tropical storm watch is a good call as they will reside in the eastern quadrant which currently contains the highest winds. Below is the 18z track guidance for Maria for those interested.
What lies ahead?
There is currently a rather potent convectively-coupled kelvin wave (CCKW) or for lay-persons. . .enhanced thunderstorm activity. . .propagating across the Pacific. This will enter the Atlantic basin around 9/20, so until that time, the tropics should be quiet. Models are hinting at some fun and games by early next week along the East Coast though.
As you can see above, the Canadian model has a few suspect areas which I highlighted with red circles. The one nearest the southeast US coast does not look like much on here, but I think with strong easterly flow around a strong high pressure system over New England. . .this is a favored area for development. The low in the Eastern Atlantic would most likely stay out there, but the model picks up on the potential of development. Finally, pressures look low in the Caribbean (closest circle to the bottom) and will the aforementioned enhancement propagating east, I think this is likely area of development after 9/18. The black outline is the entire area you would look for trouble with a strong surface high over New England. For those keeping track, the NAO is forecast to be neutral to slightly negative. This promotes enhanced tropical activity in the Atlantic, but could also protect the East Coast from a landfall depending on the depth or position of the trough.
For your viewing pleasure, I have included the 12z GFS and 12z NOGAPS 144 hour forecast (12z (8 am EDT) on 09/19/11) above, respectively. As you can see, the Canadian model has friends with areas of interest at this time stamp. The NOGAPS has one more area of interest, but the ideas are the same. The black outline again represents the area where development looks most likely. Interestingly enough, the European model looks quite different and would feature a closed upper low forming off of New England. This would create a different pressure pattern near the East Coast than I have showed you above. It is possible that the Euro is correct here, but for now, I’m not buying it.
The next bursting pattern for the Atlantic should occur from about 09/20/11 to 10/01/11. It doesn’t mean there won’t be activity outside of this time frame, but the environment becomes most conducive in this 10 day period. I would expect about 3-4 storms, depending on the NHC naming scheme. In most seasons, the Atlantic gets one more burst in October and I see how the pattern could head that way based on the MJO forecast. Of note, the East Pacific has shutdown early again, though I could see a storm forming in the next week with that enhancement moving east. A quiet East Pacific usually signals a much more active Atlantic and the intertropical convergence zone (ITCZ) is expected to lift from the East Pacific into the Western Caribbean in the next two weeks. Food for thought: The GFS has storm-a-ganza occurring between the 20th and 30th, so that model senses the changes on the way.
And now for something completely different
The above image shows the enhanced thunderstorm activity in CA, AZ, and northwestern Mexico. There are a number of supercell thunderstorms in this image with the one near the Gulf of California (largest storm near the bottom) moving right, indicating strong rotation. This is highly unusual in this region and is part of the evolving synoptic pattern that is allowing cooler temperatures to spread from the Northern Plains to the Northeast. I can’t remember seeing such strong thunderstorms in this area. . .it’s the desert!
If you live in the Great Lakes, New England, and Mid-Atlantic. . .get ready for some very Fall (if not downright cold) temperatures toward the weekend. Highs in the 60s and lows in the upper 40s to around 50! Here comes winter. . .
Thanks for reading!