A few weeks ago, a strong disturbance developed in the southwest Caribbean Sea. Models had been predicting development weeks in advance, indicating a possible Florida threat. But the disturbance dissipated just about as quickly as it developed. Now, a new disturbance has developed in the same area of the southwest Caribbean north of Costa Rica. The National Hurricane Center has identified the disturbance as Invest 97L. At ImpactWeather, we’ve identified the disturbance as the 70th disturbance of the 2009 hurricane season.
The satellite image above shows the relative location of the disturbance. One can clearly see a fairly strong rotation evident in satellite loops. Surface observations do indicate the presence of a low-level circulation. That, and the presence of thunderstorms near the center, is nearly enough to classify this low pressure area as a tropical depression. But the NHC is waiting to see if the thunderstorms are able to persist for another 12-24 hours before upgrading the disturbance. A recon plane is scheduled to investigate the disturbance on Wednesday afternoon.
Computer models typically have a hard time forecasting the movement of such weak systems. And the model have a very hard time predicting (correctly) development in the southwest Caribbean Sea this time of the year. It seems that the models get confused by the ever-present thunderstorms and general low pressure in the region. So we see a lot of false alarms both early in the season (May/June) and late in the season (October/November). But out of curiosity, let’s look at where some of the non-tropical “global” models are taking this feature.
Both the American (GFS) model and the European (ECMWF) model take the system northwestward toward the Yucatan Peninsula in about 6-7 days. The Canadian model, which isn’t shown above, also takes the system northwestward generally toward the Yucatan Peninsula by early next week. The only pure tropical model that’s being run, the GFDL, takes the low slowly northward for 5 days to just south of central Cuba - as a hurricane. We’ve seen considerable differences in the models, and even in the same model from run to run over the past 3-4 days, so confidence in the track of this disturbance is on the low side.
Sometimes, climatology can give us a clue as to where a system will track. Looking back at all of the November tropical cyclones in the Atlantic Basin that developed during the month of November from1851-2006, we can see that there are two most likely tracks. Most storms developing in the southwest Caribbean either moved west or northwestward into Central America and/or Mexico and dissipated or they tracked north and northeastward, threatening Cuba, south Florida, or the Bahamas. As an interesting side note, my coworker, Dante Diaz informs me that only 4 hurricanes have struck the U.S. during the month of November. Where did they strike, you ask? All four struck Florida.
It appears that the various model runs are pretty much in line with climatology. I’m not really sure where this disturbance will track. I do think that the chances of it becoming at least Tropical Storm Ida are greater than 50%. And I’m fairly confident that it’s not going to go anywhere very quickly. I think that a Northwest Track toward the Yucatan, similar to the American GFS model may be most likely. Climatology suggests such a track. On that track, interactions with land combined with increasing wind shear north of 18N would very likely lead to dissipation. But I cannot completely discount the GFDL model which takes the low due north for 5 days to just south of Cuba as a hurricane next Sunday. If such a track does materialize, I’d think that interactions with Cuba along with increasing wind shear north of Cuba would lead to considerable weakening prior to any impact on Florida or the Bahamas.
Check back here later this week for an update on this disturbance. With any luck, this will be the last tropical threat of the 2009 hurricane season.
