FLHurricane.com: Irene Moving Northwest, TD 10 Forms

Update coming shortly on the main page (blog) with regards to the future courses and intensities of Irene and soon-to-be TD 10. I was going to try summarizing things for brevity here, but instead, here's the full version...

Irene is undergoing a little bit of easterly wind shear right now, but not a lot. The low-level center is near the deepest convection on the eastern side of the system, suggesting that it is much more vertically coherent than before. The effects of the dry environment are still present, but lessening with time. Unfortunately, we do not have a recent microwave imager pass to give us additional data since the last recon fix about 2-3hr ago, but the overall visible and infrared satellite imagery suggests the storm is getting better organized and will likely become a hurricane in the next 6-12hr. This storm may try to peak in intensity similar to Jeanne -- it does have a similar appearance on satellite imagery, for what little that is worth -- but I still feel that cat 1/2 intensity is a more likely bet.

Path? That's the million dollar question of the evening. Satellite-derived products hint at a weakness still in the ridge near where Irene is right now, but the main shortwave trough creating this weakness is about to pass the storm on by. Steering currents get pretty weak from here, as the main band of westerly flow has moved back to the north over the course of the day. An upper-low to the southwest of the storm likely interacted with it for a period of time earlier today, resulting in a temporary movement back towards the west-northwest. Overall, however, a general 300-315deg motion is what we've seen for the past day or two. There are signs of the ridge trying to build in a bit to the north of the storm, but whatever is going on there right now is relatively weak at this time.

Given all of this, a slow deceleration of the storm as it moves northwest is likely over the next 2-3 days. It should slow to nearly stationary sometime this weekend, but I do not believe that it will occur near 70W, as the 5pm package advertises. More likely, the storm will draw a bit closer to shore -- perhaps close to 72 or 73W -- before slowing down. The upper-low that has been in the Gulf is showing signs of lifting northward; as it does, in conjunction with a digging trough in the west with a shortwave moving through Idaho at this time, the flow should amplify to some degree in the east...likely with a narrow trough along the east coast and ridging further out to sea. No scenario is certain at this point in time by any means, but the threat south of Charleston is over and decreasing to the north of there. I believe the storm will remain offshore, perhaps brushing the coastline from 200-300 miles away, and ultimately move out to sea in the westerly flow. Given the strength of the westerly flow, I don't currently put much stock in the solution of it slowing and cutting off north of Bermuda in 5-6 days.

Nevertheless, everyone from Charleston northward should continue to watch this storm, as any prolonged movement to the west increases the threat to the coast. This may prove to be a close call -- with an amplifying flow pattern to potentially thank for that -- and the track is subject to change.

Invest 96L continues to become better organized, with well-defined mid-level banding features apparent on infrared satellite imagery over the past two hours. The mid- & low-level centers appear to be congealing near 13N/42.5W and I expect a tropical depression to form here within the next 12-18hr. Intensification should be modest through the forecast period as the storm moves in a general west-northwest fashion. I believe we will likely have T.S. Jose by the end of the weekend, with only some dry air and modest shear being the inhibiting factors through Monday. This is the feature the and, to a lesser degree, some of the globals (GFS & UKMET) picked up on for development over the past 4-5 days.

Unless it almost immediately begins to turn northwest and north, this developing system should continue on a general westward path. A trough is just north of the system right now, likely amplified a bit by the ridge that has been building near Irene over the past few days, but is rather weak and does not appear as a strong entity in any of the satellite-derived wind products. If it does not get captured by this, the storm should continue on a west to west-northwestward path, bringing it to near the central Lesser Antilles near the start of the week. Where it goes from there depends upon how the ridge builds in once Irene heads on out to sea...the greater the weakness left, the more likely that this system gets pulled northward across some of the Greater Antilles. Model guidance is split on solutions in the short-term with this one, but given the trends of the storm so far and climatology, slow intensification and a general west-northwestward motion is the call for now.

We'll watch the wave just off of the coast of Africa for development over the weekend as well. It's a vertically deep system already, but is rather far to the north. Given this, unless it reforms further south, it would likely be a fish spinner...moreso the faster it develops. It needs some time to get its act together before becoming a threat to do any development, but is in a favorable environment to do so. Possibly invest 97L sometime over the weekend, maybe more later on. Not much model support -- there's more for the next wave in the series -- but worth watching nonetheless. Models are calling for ridging to take over most of the basin by 5-6 days out, suggesting that things are likely to get cranking by then...if not sooner.

East Pacific is still cranking, with Fernanda still going strong -- albeit not for much longer; the deep convection is already starting to fade away on the western side of the circulation and visible satellite imagery suggests that the low-level stratocu field of the cooler waters of the Pacific may be impacting the surface circulation. The satellite representation remains very good, but I've got a feeling the strongest winds aren't making it down to the surface anymore. Expect the intensity to start falling at a good clip over the next few days. As it weakens, the overall environment for Greg should become a bit more favorable; slow intensification is likely with this one. They'll both keep heading west, likely to kick up some surf for Hawaii down the line (but nothing more at this time). The feature just off of the Mexican coast also is a candidate for development as it moves parallel to coast; would not be surprised to see it perk up into an invest/depression this weekend as well.

Prime time is beginning, as advertised. Stay tuned, as this may just be the tip of the iceberg.

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