berrywr
(Weather Analyst)
Thu Aug 05 2010 09:58 AM
Re: Ex-Colin Flares Up Again

As I stated in my post; while it looks impressive on satellite at any given point in time doesn't mean it can sustain itself for any length of time and such is the case this evening and morning. The first chart forecasters like myself look at is the Wind Shear Analysis and for the moment the remains of Colin are embedded in winds aloft of 20 to 30 as high as 40 knots aloft. While 20 isn't death, 30 to 40 knots is for any tropical system to gain in vertical depth and organization. When I was in school the hardest thing I had to do when analyzing clouds were which ones were shallow, mid and upper level and determine what directions each of those elements were. Ed makes a good point about this in his met discussions....because there isn't a surface low does not mean there is no rotation within the system; it may be broad, it may be a remnant low or simply non-tropical; however in the mid and upper levels there is usually rotation. When mets refer to shear they normally are talking about winds at 300 millibars or 30,000 feet MSL. There is low level shear as was the case a couple of days ago; the Low Level Easterly Jet which can only be found in the Tropics. You may remember that the system was moving incredibly fast...30 mph which in and of itself is shear which in fact disrupted the system's surface circulation. Whatever becomes of this system for the near term is not a threat to the US with a TUTT oriented NE to SW acting like a big wall. Not to be too technical; we're currently in what mets call a 5 wave pattern; that is 5 longwave troughs around the globe. This pattern is generally progressive, that is there on the move; generally west to east. Long range models continue to reflect the Mid-Continental Upper Ridge to be in place...slightly weaken...re-strengthen and weaken ever so slightly again but retrograde further to the west allowing a longwave trough to set up shop near the East Coast. What this means is the East Coast is closed for business for the near future out at least one week. There will be a narrow opportunity for this system to become a depression as it moves NW in about 36 to 48 hours. Between now and then; doubtful though it won't be at all uncommon to see some big thunderstorms go up. What matters is can they be sustained. At the trough axis there is a clear dividing line between dry and subsidence air and rising and moist air; typical of tropical waves.


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