10/2/05 FCST: Hurricane Stan (dissipated)

Jul 18, 2004
Westport, CT
Well that mess in the wrn Caribbean that was Invest 99L has been officially classified as TD20 as of the 15z advisory. Currently centered at 19.3N 85.8W, the depression is located just offshore of the Yucatan Peninsula of Mexico. Good outflow is being exhibited and the depression will continue to be located in an area favorable for development; land interaction should be the only hinderance to strengthening in the short term. The system is currently in an area of weak steering currents, but this should change in the next 12 hours or so, and a general WNW movement should begin by that time.

Once the system exits the Yucatan, the condition will likely remain favorable for intensification and the 12z SHIPS guidance brings 20 up to 91kts by 120hrs. On the other hand, the GFDL shows nearly the opposite, with the depression dissipating over land in the next 24-36hrs. As is usually the case, if the depression can survive its trip over the relatively flat Yucatan, then this will become a rather serious threat to points to the west.

At this time, all indications are that the ridge to the north will hold strong, thus keeping the cyclone on a general W/WNW track for the remainder of its life. However, if a weakness develops or the high moves to the east, 20 could take a more NWerly track...but we'll just have to wait and see.
The depression has continued to get better organized over the past several hours, and the system is comprised of several curved bands of convection, mainly to the east of the center. Outflow is still excellent in most quadrants, most notably so in the entire eastern semicircle. The latest Dvorak classification at 2345z was T2.0 or 30kts, and the 0115z UW-CIMMS satellite-based intensity estimate was T2.3 or 33kts. Based on this information and the fact that the recon flight which took off about an hour ago won't reach the system until 05z, the 03z update will likely maintain this system as a depression just below tropical storm strength.

As far as intensity is concerned, it is quite likely that the depression will achieve TS status before making landfall on the Yucatan (the recon flight will probably find a system named Stan when they get there later tonight). Once it traverses the Yucatan, intensification seems likely and the 00z SHIPS model brings the depression up to 93kts in 4 days, though the 18z GFDL is far more conservative. If a strong inner core can become established before it reaches the Yucatan, then reintensification will be likely once the system reaches the Bay of Campeche. Seeing as the cyclone has been steadily becoming better organized, the SHIPS scenario seems the most plausible at this time.

As it stands right now, the cyclone should move on a general WNW track across the Yucatan and into the BoC before coming ashore over NErn Mexico. Unfortunately for us Americans, some of the models are starting to hint at a significant stall over the southern Bay of Campeche before pulling 20L back to the north. Though it is unclear whether this will occur, climatology suggests that systems around this time of year in the GoM/BoC have a hard time maintaining a westerly heading for an extended period of time, as frequent troughs tend to dig down and pull things back the north.

The bottom line is that TD20 should be upgraded to a TS at 06z, and that, if it can cross the Yucatan with minimal disruption, it poses at least a marginal threat the the US Gulf Coast down the road.
From the USAF hurricane hunter flight level data update at 0623z this morning:

0621 1807N 08701W 01525 0028 207 051 01591 0000000000

This 51kt FL measurement was the basis for the upgrade to TS status at 0635z, though these winds are occurring in an area of deep convection well SE of the center (~100nm).

Other than that, very little has changed in the last few hours except for the fact that 20L has begun moving consistently to the WNW and the center is very close to the coast of the Yucatan Peninsula.
Well the center of TS Stan (probably down to a TD at 21z) is still inland over the Yucatan Peninsula of Mexico, though it appears to be N of the 15z forecast point. The models are in very good agreement that the system will continue on a general westerly course before making landfall over NErn Mexico in about 48hrs.

The 18z SHIPS model is still being bullish with the intensity forecast for 20L, bringing it to hurricane strength before the 2nd landfall; the GFDL is still maintaining that Stan will only undergo modest intensification. With very warm SSTs in the BoC (>31C) and light vertical shear for at least the next 24-36 hours, and given that the LLC seems to be faring pretty well over land, I think the SHIPS solution is the most proable.