Subtropical Storm Ana

The NHC has issued its first advisory on the season's first subtropical storm - ANA.

BULLETIN SUBTROPICAL STORM ANA ADVISORY NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012015

1100 PM EDT THU MAY 07 2015
...SUBTROPICAL STORM ANA FORMS OFF THE SOUTHEAST U.S. COAST...

SUMMARY OF 1100 PM EDT...0300 UTC...INFORMATION
ABOUT 170 MI...275 KM SSE OF MYRTLE BEACH SOUTH CAROLINA
LOCATION...31.5N 77.6W

MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...N OR 350 DEGREES AT 2 MPH...4 KM/H

A TROPICAL STORM WATCH HAS BEEN ISSUED FROM EDISTO BEACH SOUTH CAROLINA 
TO CAPE LOOKOUT NORTH CAROLINA. A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA, GENERALLY WITHIN 48 HOURS..

ANA is expected to intensify a bit before making landfall  over the coast of the  over the weekend and it could acquire tropical features as it moves slowly over the warm waters of the Gulfstream current.  

Radius of maximum winds and Tropical Storm Watch area

Strongest winds are displaced well away from the center but in time are expected to draw closer to the center of circulation.

Radar and track of Ana thus far

 Some of the heavier showers are flirting with the coast of North and South Carolina.

TC guidance tracks

Cyclone track guidance is in very good agreement for Ana to turn NW and make landfall on the South Carolina coast and then turn northeastward  late in the weekend through early next week. The system could prove to be a beneficial rain producer for parts  of the Easter U.S. including NY States

Below is the forecast track from the NHC. Once Ana makes landfll it is expected to weaken considerably. 

Official NHC forecast track for Ana

Hurricane Reconnaissance Ongoing

An Air Force hurricane recon aircraft is currently flying in and around the area of low pressure off the Southeast U.S. coast. So far based on the observations the strongest winds are almost 30 mph and the lowest observed pressure is around 1007 millibars, at best its intensity is that of a weak (sub)tropical depression. (NOTE: As of around 245 PM EDT to the north and northeast of the low (over the Atlantic) winds of 40-45 mph have been recorded by the aircraft)

Above is a bar chart of the wind (red bars) and pressure data (blue bars) plotted versus  the time along the bottom horizontal (x -axis).

The satellite presentation is also a bit better this afternoon as evidenced by a more circular appearance to the cloud features with respect to the surface low's location approximately 200 miles to the SSE of the SC/NC border.





Some of the rain associated with the low is already affecting parts of the Southeast coast and more rain is expected to fall over the next few days.

The low is expected to continue to slowly develop with  The NHC now giving a HIGH 80% probability for the low to become a subtropical depression or storm.

It is forecast to move toward the N-NW through the weekend and will likely cause moderately strong winds and spread heavy rain, rough surf and higher than normal tides to the coasts of North and South Carolina south to Georgia and the Florida east coast, too.

If the system attains winds of 40 mph or more, whether its subtropical or tropical it will be named  Ana.

A Quick Update on the Low developing off the SE U.S. Coast

The system hasn't really developed much. Strong wind  shear aloft is causing the showers and storms to be displaced from the actually surface low center. This asymmetric structure to the clouds and showers being "removed"  from the actual is typical for subtropical systems.

This asymmetric structure to the clouds and showers being "removed"from the actual is typical for subtropical systems. (Where as a tropical system exhibits  more symmetry - clouds/showers are  concentric with respect to the low pressure center as is the wind field, too.) The guidance data is varying from one forecast cycle to another.

The latest tropical cyclone guidance is now leaning more toward a motion initially toward the north followed by a gradual turn northwest toward the SC/NC coastline. (map below)

TC Guidance

The ensemble data for the tropical models as well as from the GFS ensemble suite are also leaning toward a north track then bending back towards the SEUS coast.

TC Guidance Ensembles

GFS Ensembles (GEFS) for low off the SEUS Coast

Even more different is the actual GFS operational (OP) run that takes the low north then nearly due west to a landfall on the Georgia coast over the weekend. The movie loop below is the GFS "OP" run :

In general folks along the SEUS coast should continue to keep tabs on this system through the weekend. The system will bring gusty winds, heavy ran and rough surf with rip currents to the Carolina coasts south the Georgia and Florida, too over the next 3-4 days. And the system could strengthen into a weak subtropical or tropical storm with winds of perhaps 40-50 mph. 

Forecast Quiet Hurricane Season Could Start Early

Satellite imagery is showing a sprawling area of clouds off the East Coast of Florida. At the surface a trough of low pressure extends from north of Cuba through the Bahamas.  This area is expected to gradually organize into a low pressure area over the next few days.



The National Center in Miami is issuing a medium (40%-60% ) chance for this system to organize into a potential subtropical cyclone over the next 48 to 96 hours.

The system is expected to bring some beneficial rains to South Florida and also produce some rough surf along its east coast northward to the Georgia and Carolina's shoreline as well as dangerous rip currents.
I mentioned in the title of this post it is expected to be a rather quiet hurricane season in the Atlantic this year.  Colorado State University has come out with its first outlook for the season.

The reason for an inactive season a moderate to strong El Nino is expected and Atlantic Ocean water temperatures are averaging colder than normal. Just a note of caution - this outlook doesn't mean that storms won't affect the U.S. Mainland. So due diligence is still needed for residents along the U.S. coast from Texas to Maine.