Tropical Storm Andrea Provides an Opportunity to Examine Potential Boundary Interaction, a Possible PRE, and Cold Air Damming

andrea.03z

Regional reflectivity imagery from ~03Z 2013/06/06 highlighting the convection associated with Andrea across central and southern Florida and more scattered convection across the Southeast associated with a stalled frontal zone.

The CSTAR Tropical Cyclone QPF/Boundary Interaction project has been examining Tropical Strom Ernesto from August/September 2006. Tropical Storm Ernesto was a modest tropical cyclone that interacted with a fairly strong boundary across the Southeast. Jordan Dale from NC State has been investigating the role of a Predecessor Rain Event (PRE) on the development of cold air damming, frontal position, and eventual track/rainfall associated with Hurricane Ernesto.

The development of Tropical Storm Andrea late this afternoon and its anticipated track across the Southeast appears to provide another case where a tropical cyclone interacts with a larger scale frontal zone, where there is potential for fairly significant precipitation possibly meeting the definition of a PRE, and the potential for cold air damming across portions of the Carolinas and Virginia.

Earlier on Wednesday before Andrea was officially named, Weather Prediction Center (WPC) noted the development of weak cold air damming and how it may influence the track of the low…

SHEARED CONVECTIVE LOW MOVING UP THE EAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE:  12Z UKMET/00Z ECMWF BY DEFAULT
CONFIDENCE:  AVERAGE

THERE IS QUITE A BIT OF SPREAD WITH THIS SYSTEM.  THE 12Z NAM/09Z SREF MEAN ARE THE FARTHEST TO THE LEFT, ALLOWING THE SYSTEM TO CROSS MID-LEVEL HEIGHT AND 1000-500 HPA THICKNESS LINES MOVING IT CLOSE TO THE APPALACHIANS.  THE OTHER GUIDANCE IS QUITE DIFFERENT, ALLOWING THE SYSTEM TO ESCAPE ALONG A COASTAL ROUTE, WITH THE 12Z GFS THE QUICKEST, THOUGH IT HAS SLOWED DOWN SOME OVER ITS PAST DAY OF RUNS.  THE 12Z UKMET IS THE SLOWEST.  SINCE THE SYSTEM IS EXPECTED TO MAINTAIN AN AREA OF THUNDERSTORMS FAIRLY CLOSE TO ITS
CIRCULATION CENTER, IT SHOULD NOT BE OCCLUDING/CROSSING MID-LEVEL HEIGHT AND THICKNESS LINES, WHICH RULES OUT THE NAM/SREF MEAN SOLUTIONS.  A COASTAL ROUTE LOOKS BEST AS A WEAK RIDGE OF HIGH PRESSURE SHOULD BECOME REINFORCED BY THE SYSTEM’S INCREASINGLY COMMA HEAD RAIN PATTERN, ESTABLISHING THE WEAKER FORM OF COLD AIR DAMMING EAST OF THE APPALACHIANS AND DIVERTING ITS TRACK TOWARDS THE COAST.  THE 00Z GLOBAL ENSEMBLE GUIDANCE SHOWS SPREAD AS WELL, WITH THE GEFS MEMBERS OUTPACING THE ECMWF/CANADIAN ENSEMBLE MEMBERS.  THE GFS/GEFS MEMBERS CAN TRACK SYSTEMS WHICH HAVE YET TO ORGANIZE INTO TROPICAL/SUBTROPICAL CYCLONES TOO QUICKLY, AND THE ECMWF GUIDANCE TENDS TO ACCELERATE SYSTEMS INTO THE WESTERLIES TOO SLOWLY.  THE PIECES OF GUIDANCE ON THE QUICK SIDE OF THE ECMWF MEMBERS AND SLOW SIDE OF THE GEFS MEMBERS ARE THE 00Z ECMWF/12Z UKMET.  THE 17Z MEDIUM RANGE COORDINATION CALL WITH THE NATIONAL HURRICANE CENTER — NHC — CONFIRMED THIS IDEA.  THE 00Z ECMWF/12Z UKMET ARE PREFERRED HERE WITH AVERAGE CONFIDENCE CONSIDERING ITS PROGRESSIVE NATURE.  CONSULT NATIONAL HURRICANE CENTER (NHC) TROPICAL WEATHER OUTLOOKS FOR THE LATEST ON ITS CURRENT DEVELOPMENTAL STATUS/CYCLONE PHASE.

Also, NESDIS put out a precipitation discussion this afternoon referencing a possible PRE associated with disorganized convection over SC during the afternoon…

EVENT…WEAK PRE SIGNAL…LOTS OF BOUNDARIES…INCREASING MOISTURE…WEAK DISTURBANCE FOR LOCALLY HVY RAINS ALONG BOUNDARIES…MORE RAINFALL FOR
THURSDAY INTO FRIDAY…
.
SATELLITE ANALYSIS AND TRENDS…VERY HIGH MOISTURE IN THE EASTERN GULF OF MEXICO AT CLOSE TO 2.6″ PWAT OR 160 PERCENT OF NORMAL WAS SHOWING SOME WEAK ADVECTION INTO GEORGIA AND SOUTH CAROLINA AT 700MB FLOW. VARIOUS BOUNDARIES WERE ACROSS THE AREA TO ALLOW FOR A LITTLE BETTER FOCUS TO HEAVY RAINFALL.  MID/UPPER LEVEL WINDS WERE GENERALLY 10- 20KTS SO THAT MOVEMENT OF CELLS WERE MOVING BUT COULD STILL PUT DOWN A QUICK 0.5″-1.5″ IN A AN HR TIME PERIOD.  ALL THESE FACTORS NOT QUITE ADDING UP TO IDEAL PREDECESSOR RAINFALL EVENT (PRE) CONDITIONS…BUT COULD IN SOME ISOLATED PLACES ALLOW FOR THE MAIN CRITERIA TO BE MET OF 4″ PER 24HRS. AT THE MOMENT…N-S CONVECTIVE OUTFLOW WAS PUSHING WEST ACROSS E CENTRAL AND SE GEORGIA FOR SOME LOCALLY HVY RAIN THERE.  MORE OF A FRONTAL BOUNDARY WAS HELPING IGNITING CONVECTION ACROSS FAR SOUTHERN GEORGIA WEST INTO EXT SE ALABAMA INTO THE FL PANHANDLE.   AND AN ELEVATED BOUNDARY WAS AFFECTING CENTRAL SOUTH CAROLINA AND INTERACTING WITH THE NORTHERN PORTION OF THE SEA BREEZE BOUNDARY IN CENTRAL SOUTH CAROLINA MENTIONED ABOVE.    COLDEST CLOUD TOP AT -60C ASSOCIATED WITH OVERSHOOTING CLOUD TOP NEAR AIKEN COUNTY WAS ALSO HELPED ALONG BY MERGER AND JUST NORTH OF THE NOSE OF THE GOES WATER VAPOR JET LET CROSSING SOUTHERN GEORGIA WEAK SHORT WAVE THAT HAS RECENTLY PASSED FROM EASTERN GEORGIA INTO SOUTH CAROLINA

Participants in the CSTAR Tropical Cyclone QPF/Boundary Interaction project will be watching this event during the next few days as it provides an excellent real time case to examine.

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