Tropical Weather Update 8/19/11
Tropical Depression #8
Aircraft reconnaissance flew into TD 8 this morning and found a system that was a borderline depression/storm. The plane found a minimum pressure of 1004mb and FL winds of 35 knots with SFMR readings as high as 45 knots. The NHC could have upgraded this to Harvey and I would have had no qualms with it. The center fixes were a little north of where the 8am advisory had the storm center and this is important as it looks like the storm center is going to avoid moving onshore along the northern Honduran coast and stay over water. This will give the storm about a 24-36 hour window for intensification and it seems likely that it will become a tropical storm probably later today.
The forecast seems to be rather straightforward. A strong ridge to the north of the storm will keep it on a slightly north of west motion and this system should plow into the Belize coast and likely die over Guatemala or Mexico. I think this will become Harvey and could become a strong tropical storm before landfall with winds in the 55-65mph range. I don’t think it has enough time to become a hurricane.
The saga of this system seems destined to last a while. It does appear to be getting better organized the NHC has raised development chances to 40% as of 8am. Convection has increased and it appears to have a curved band appearance on satellite imagery. I still do not expect rapid intensification over the next few days, but it could become a depression by Sunday or Monday. Model guidance is consistent in showing a W to WNW track bringing the system into the central Islands by Sunday and into the northeast Caribbean early next week. Then the guidance starts to diverge.
To put it simply the global models have been all over the place ranging from the Houston to a re-curve off the Carolina coastline. There are many variables to this forecast which make it very difficult to come up with a strong handle. A general WNW track is likely through the next few days and this should bring the system very near or over Puerto Rico and/or Hispaniola in several days. The tropical intensity models show the storm as a strong tropical storm to low end hurricane at the time this happens and I could see that.
Beyond that it will depend exactly on how the storm moves in relation to the Greater Antilles. A track across Hispaniola and Cuba could leave little left of the system. However a track just south could lead to a strong system as it traverses the high heat content waters of the Caribbean. Eventually the models agree on a strong trough forming in the eastern US and likely picking up this system and turning it poleward. If the more southerly track materializes than we would see a threat to the eastern and central Gulf Coast. If a more northerly track develops than the threat would be more for south Florida and the southeast coast.
The 00z ECMWF was showing a Gulf threat in yesterday’s 12z cycle, but the 00z is further east again showing a landfall in southeast Florida and then a close pass off the southeast coast and what looks to be a turn to the north at the very end as a trough dives in from the Midwest that would threaten the mid-Atlantic coast possibly after day 10. The 00z GGEM shows a similar track to the 00z ECMWF. The 6z GFS showed a track into the eastern Gulf and then the trough capturing it and turning it NE into the FL panhandle and across the southeast US and the 12z GFS shows a similar track with landfall in Pensacola.
All and all not a lot has changed since yesterday. I still expect this to develop later than sooner and probably threaten the US. Florida seems to stand the highest chance of a hit, but I am not so confident on west vs. east coast of Florida. Stay tuned over the weekend. My feeling is that I have a hard time seeing this going any further west than Mobile Bay with the progged upper air pattern.
It is possible that this wave could develop faster than invest 97. It is pretty well organized at this point with a well-defined circulation and decent convection. Models take this system to around 16-18N by the time it reaches 30W, which is historically usually too far north to ever be a US threat.
However, we have to see if this is actually going to happen, and even it does, the models show a very strong ridge to the north that should turn it to the west in several days and keep a mostly west track for a while. The models do eventually re-curve it out to sea probably with the same trough which could capture Invest97 next weekend.
A key for this system could be the next few days to see how much latitude it gains. One thing is for sure, right on time the Atlantic is gearing up.