12:25 PM | Odds favor Tropical Storm Karl curving away before ever getting too close to the US, but it still needs to be closely monitored as a small shift could have an important impact
Paul Dorian
00Z GFS 500 mb geopotential height and anomaly forecast map for Sunday monring, September 25th; courtesy tropicaltidbits.com, NOAA
Overview
Tropical Storm Karl continues to churn to the west today in the central Atlantic Ocean and it could very well reach hurricane status by the early part of the weekend and be situated somewhere between the Bahamas and Bermuda. Meanwhile, a deep upper-level trough of low pressure will be slowly pushing eastward to southeastern Canada at this time and this feature will become a crucial player in the eventual storm track of Karl. Latest computer model forecasts strongly suggest Karl will get influenced by the upper-level trough and driven to the northeast away from the US coastline; however, it still needs to be closely monitored as a small shift in the timing of weather systems can result in quite a different outcome.
Latest GOES visible satellite image of the Atlantic Ocean with Tropical Storm Karl (circled); image courtesy Penn State eWall, NOAA
Latest storm info
The latest readings on Tropical Storm Karl indicate that the max sustained winds are 40 mph and the movement continues to be westerly at 13 mph. The latest satellite image shows a somewhat disorganized system with convection separated from the main area of low-level circulation. Some vertical wind shear and dry air is currently inhibiting any possible strengthening of Karl and will likely continue to do so over the next couple of days. After that, the wind shear is likely to decrease, mid-level moisture is likely to increase, and intensification in days 3-5 could very well propel Karl to hurricane status by the weekend.
00 GFS Ensemble forecasts of storm track of Karl over the next several days; map courtesy Weather Underground, NOAA
Computer model forecasts
Most computer forecast models agree that a deep upper-level trough of low pressure will slide across southeastern Canada by the latter part of the weekend. According to most medium-range model operational and ensemble forecasts, southwesterly winds on the front side of this trough will act to stop Karl in its progression towards the US east coast and re-curve it back to the northeast out into the open Atlantic. Last night’s 00Z operational GFS model run for Sunday morning, September 25th, shows this deep upper-level trough and an extension of the trough representing Karl (indicated by the arrow) as it gets “absorbed” into the southwesterly flow of air associated with the front portion of the eastward moving trough. In addition, last night’s GFS ensemble forecasts of the storm track for Karl uniformly suggest that Karl will re-curve to the northeast before ever coming close to the US east coast.
While odds favor this scenario, the forecast of a re-curve is no guarantee and it wouldn’t take much of a small shift in the current timing of various systems in the atmosphere for Karl to “slip” underneath the trough and continue on its way closer to the US east coast. If Karl could “slip” underneath Karl, the next major player in the atmosphere would be another deep trough of low pressure headed towards the central US by the middle of next week and that location would allow for Karl to meander closer to the coastline should it not re-curve to the northeast with the first upper-level trough. Stay tuned.
Meteorologist Paul Dorian
Vencore, Inc.