Tropical Update 8/17/11
There are some signs this morning that Invest93 is getting a little better organized, although certainly not rapidly. The satellite signature now shows a curved band of convection and what looks like the possibility of a twist in the cloud cover. The clouds top temperatures though on IR satellite imagery are not very impressive and the convection is somewhat limited. In looking at the latest buoy/ship obs in the Caribbean, the closest buoy has shown a pressure around 1011mb with east winds around 20 knots. So Invest93 is not near depression strength yet, but it is probably closer than it was yesterday. The 8am NHC outlook raised development chances to 30%.
As I mentioned yesterday, the weaker Invest93 stayed the better chance we would see the further south track scenario occur. Indeed most all of the model guidance is now showing the system into Honduras and Nicaragua in the next 48 hours and never really re-emerging. It is possible if the track trended north a bit, it could stay over water a little longer and then hit Belize. In any event the system has about 48-60 hours to get it’s act together before it would plow onshore. I give it a 50/50 chance as of this morning of getting a name before landfall in Central America. It likely will not re-emerge into the Gulf, so it looks to be absolutely no threat to the US as of now.
The system near 30-35W has still not gotten its act together as of this morning. There appears to be a broad cyclonic twist near 13N/33W or so but convection is limited. There is convection to the south of this twist associated with the ITCZ. It is possible that we could see this consolidate into one low pressure area with more convection in the next day or so, but any event rapid development does not look likely.
Neither the GFS nor ECMWF show much development with this system over the next 48-72 hours and with the current state of the system, I would agree with that. As it approaches the Islands this weekend the GFS does show development into a tropical storm by Saturday while the ECMWF still shows mostly a wave. They both take the system through the northern Islands, with the GFS a bit further south than the Euro and stronger on Sunday. By Monday the GFS has a strong tropical storm very near if not passing over Hispaniola, while the ECMWF also shows some strengthening as it passes just north of Hispaniola. Both models than move the system into the southern and central Bahamas by Wednesday with the GFS strengthening the system and implying a strong tropical storm or weak hurricane while the ECMWF shows a moderate tropical storm. The GFS moves the system across south Florida as a minimal hurricane and then into the eastern Gulf with a turn to the north and another landfall in the eastern Gulf. The ECMWF shows the system though turning north off the Florida coast by late next week.
That is what the models literally show now what will really happen? I think the system will slowly get organized over the next few days as it moves west towards the Islands. I don’t see it becoming a depression or storm before the weekend but it could over the weekend. The strong ridge to the north will steer the system generally WNW and I think there is a good chance it is around 25N/75W by mid next week. By early next week the system will be on the western flank of the north Atlantic ridge and this could be a favorable location for development. Thus the storm may be a late bloomer with most of the intensification occurring west of 65W. The global models are in good agreement on a solid trough over the Great Lakes and northeast US mid to late next week. So unless the system stays so weak that it goes into the Caribbean around 15-17N, it should start to turn northwest. However, the models also show this trough lifting out late next week as the western Atlantic ridge strengthens and expands toward the southeast coast. A weakness remains between the southern Plains upper ridge and western Atlantic upper ridge though and I would forecast that this system will head for that. So the issue will be how far west it gets before this happens.
Right now it seems kind of pointless to speculate until we see actual development, but that is what the pattern is looking like right now.