been watching this pattern unfold, trying to prog what would happen from days out. about a week ago i was thinking the se caribbean would supply what we would see as the early october ridge is ready to set up over the east u.s./western atlantic. idea has changed nominally as the current 99L has gone through most of the caribbean, and has slowed and is trying to develop north of honduras now. was thinking we'd have two storms to worry about next week, and i think i've got the evolution figured out now. here goes.
it's not a real development threat but just an item of interest, because the rita shear-off remnant idea worked. that little piece of energy that was deposited off the fl panhandle yesterday in rita's wake has developed a little surface low that has wended nw towards the mississippi coast today. it's weak and in a high-subsidence environment, but the little thing showed up nonetheless.
bigger concern is 99L, which is very slowly organizing into a tropical cyclone. the system has had a surface low for three days now, but convection has consistently not concentrated near the center, flaring to the east repetitively. today the overall organization is a little better, though i'd still hesitate to call it a depression. if the stuff near the center winks out overnight look for thursday to be another day in limbo with a half-formed system moving slowly wnw or nw in the caribbean. best bet is that it does finally develop. models are inconsistent with its future movement, but i'd bet on a cross-yucatan/western gulf track, and a very slow one at that. the yucatan is probably going to see flooding out of this one... and it could eventually end up in texas later next week.
the precursor is what i'm calling the system i'm expecting to form off the east coast next week. i've seen the pattern that is trying to make something be there coming for a while, but haven't been sure what trigger the system would develop around. think i've spotted it today. earlier i was looking for a wave interacting with the shortwave energy that gets left as that fast-moving frontal system moves off the east coast and lifts out over the weekend... but the wave energy to the southeast has been blown hither and yon by those elongated troughs deep in the tropical atlantic along 50-60w. a little bit of that may make it up, but now i'm becoming convinced that the little swirl firing convection near 28/73 is what will meet with the shortwave energy and get trapped under the ridge next week. a load of the globals are showing an inverted trough/hybrid system moving towards the southeast mid/late next week... nogaps in particular sees the weak little low there now (under a sheared/diffluent atmosphere as the florida upper low lifts out northeast) getting picked up briefly by the front and left behind to press against the ridge. by sunday or monday i'm expecting this to either be a closed deepening storm or a very sharp trough... and it ought to run west towards either florida or up to the carolinas depending on how much the shortwave initially grabs it and how the ridge evolves next week. i don't entirely trust the evolution since it isn't showing a tropical cyclone crossing the yucatan yet. when it gets that system in the mix i'll have a better idea where the precursor might go. if it's any hint, the typhoon (longwang.. not joking) running the ryukyu islands and chinese coast next week teleconnects to a system running westward towards the southeast).
anyhow, in case any of that's over anybody's head, here's what i'm reckoning on:
the system in the caribbean will develop and move slowly nw. may eventually target texas or north mexico later next week.
another system will likely form off the east coast and run westward as long as the ridge holds. i'm expecting it will be a tropical cyclone and that it will reach the coast also late in the week.
down the road gfs is showing more activity in the gulf/caribbean. i think it's losing a grip on the pattern past ten days, so not going to speculate yet on whether those are legit possibles.
HF 2351z28september