LC- I just posted the following on Ed Dunhams recent forum--
'Ed-- could you help us understand how a system with this type of satellite presentation is not a depression despite the calm winds at the surface. I have been tracking storms for a long time and do not remember a senario like this.'
Touches on what you are mentioning about MLC. I just don't get it!
Satellite can be very deceiving because, as it looks from the top-down and IR/visible satellite cannot look through clouds, you won't see the surface features in the midst of a region of convection. IR satellite is generally going to be poor at looking at surface features, anyway. You can use visible satellite to track low cloud motions outside of convection during the day, but even that won't be perfect.
Ultimately, though, convection like that which we've seen with 92L is a conduit for a lot of heat release in the mid-upper levels of the atmosphere. That helps spawn a mid-level vortex/circulation, often also referred to as a mesoscale convective vortex (MCV), in those levels. This heating will help force lower surface pressures and, in some cases, the development of a low-level circulation beneath the MCV. Sometimes, though, convection will fire away from a pre-existing surface circulation, often causing there to be competing focal points for development. Heating because spread out over a large spatial extent rather than focused near one circulation (whether surface or mid-level). This can slow and hinder the development process until one feature becomes dominant.
The satellite appearance we have seen with 92L today is indicative of a healthy upper-level environment, one which has favored a convective burst to the NE of a pre-existing surface circulation. This convection helped spawn the development of an MCV around which further convection could organize. Outflow aloft is still present with these features too, giving the system the appearance of a healthy tropical system. But, alas, with no surface reflection or organization, you don't have a tropical cyclone. Often, though, these features are immediate precursors to tropical cyclone development! They are common in the Caribbean with fast-moving storms, where the storm motion is so fast to prevent there from being a closed surface circulation, and with disturbances in the deep tropical Atlantic that are in the early stages of development.
All in all, with everything but land interaction favorable, 92L is on the precipice of development...but given the limiting factors above, that's sorta how it can have the appearance that it does without yet being a tropical cyclone.
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