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05/26/2018

Sub-Tropical Storm Alberto Update

Alberto is a Sub-Tropical Storm, the first named storm of the 2018 hurricane season.  The fact that it is a tropical storm means sustained winds are between 39 mph and 73 mph.  You may have not seen the "sub" at the beginning before.  Here's a definition from the National Hurricane Center of a subtropical cyclone:

"A non-frontal low-pressure system that has characteristics of both tropical and extratropical cyclones. Like tropical cyclones, they are non-frontal, synoptic-scale cyclones that originate over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center. In addition, they have organized moderate to deep convection, but lack a central dense overcast. Unlike tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources, and are generally cold-core in the upper troposphere, often being associated with an upper-level low or trough. In comparison to tropical cyclones, these systems generally have a radius of maximum winds occurring relatively far from the center (usually greater than 60 n mi), and generally have a less symmetric wind field and distribution of convection."

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Alberto threatens the Gulf coast states with heavy rain, gusty wind, storm surge, inland flooding, and isolated tornadoes/water spouts.  The remnants of this system will make it to Kentuckiana, but it will not carry the same threats by the time it gets here. 

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We will see breezy and rainy conditions Wednesday and Thursday.  Alberto will be a weak low pressure (not a tropical storm) when it gets here, but it will still bring an inch or two of rain.  We expect higher rain totals south and smaller amounts north since this system is moving up from the south. 

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Below is text discussion from the National Hurricane Center's latest update issued at 5 PM Eastern:

Before departing the storm, the Air Force Reserve Hurricane Hunter aircraft flew near the low-level cloud swirl that became apparent in visible satellite imagery over the southeastern Gulf of Mexico late this morning. Data from the plane indicate that the center had reformed in that location and that the pressure had fallen to 999 mb. The aircraft did not sample the area to the east of the new center, but based on recent satellite classifications and surface observations the initial intensity remains 35 kt for this advisory.

The primary mechanism for intensification appears to be a shortwave trough moving southeastward into the larger negatively tilted trough over the eastern Gulf, which should cause a cutoff low to form during the next 24 hours. This is expected to result in deepening of Alberto while it moves generally northward over the Gulf of Mexico on Sunday and Sunday night. The shear is forecast to decrease as Alberto become co-located with the upper-level low and the system could transition to a more tropical cyclone-like structure before landfall. The NHC intensity forecast once again calls for steady strengthening through 36 h, but shows little strengthening after that time due to the possibility of dry air intrusion.

The system has moved generally northward during the past 24 hours, however, the reformation of the center today makes the initial motion estimate more uncertain than normal. Alberto should move northward to north-northeastward tonight, and then turn north-northwestward and decelerate on Sunday and Sunday night as it moves around the eastern side of the trough/cutoff low. The dynamical models remain in good agreement on this scenario but have shifted eastward once again. The interpolated guidance models lie a bit west of the model fields due to the more northwestward 1800 UTC initial position of Alberto. As a result, the NHC track is along the eastern edge of the guidance envelope as a compromise between the ECMWF/GFS model fields and trackers.

The new NHC track forecast has required the issuance of a Tropical Storm Warning for a portion of the west coast of Florida and a Tropical Storm Warning for a portion of the northern Gulf Coast.

KEY MESSAGES:

1. Regardless of its exact track and intensity, Alberto is expected to produce heavy rainfall and flash flooding over western Cuba, southern Florida and the Florida Keys. Rainfall and flooding potential will increase across the central U.S. Gulf Coast region and over much of the southeastern United States beginning Sunday and will continue into next week.

2. Tropical-storm-force winds and hazardous storm surge are possible along portions of the central and eastern U.S. Gulf Coast beginning on Sunday, including areas well east of the track of Alberto's center. Residents in the warning and watch areas are encouraged not to focus on the details of the forecast track of Alberto and should follow any guidance given by their local government officials.

3. Dangerous surf and rip current conditions will likely spread northward along the eastern and northern Gulf Coast through Monday.

They also updated a Tropical Storm Watch in Florida and Alabama to a Tropical Storm Warning as the confidence grows in where Alberto will make landfall.  Watch for updates on my social media pages using the links below. 

Hannah's Facebook Page

Hannah's Twitter Page

-Hannah Strong

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