Tropical Storm Danny Spaghetti Model, Discussion-East Coast, Halifax Wary


Tropical Storm Danny 1845Z 08.25.09

Tropical Storm Danny 9:18:45Z 08.26.09

Tropical Storm Danny NHC forecast Track 11am 08.26.09

Tropical Storm Danny NHC forecast Track 11am 08.26.09

For a more recent update on Tropical Storm Danny, CLICK HERE

As hinted in a previous post, Invest 92L has indeed become Tropical Storm Danny.  The initial model runs are still holding pretty much on line.   That is some want to take it as a tropical storm or even a weak hurricane into North Carolina and then along the US coast with some deepening to as low as 985 mb somewhere between Washington DC and New York City.  Others want to have the storm brush the Carolina coast and hug the East Coast of the US and deepen before moving just east of Halifax, Nova Scotia.  Still others want to keep the storm offshore altogether before it runs into Nova Scotia.  Andrea in Halifax…all the models have it affecting you in some manner…But…

Danny Water Vapor 9:17:45Z 08.26.09

Danny Water Vapor 9:17:45Z 08.26.09

There is some consensus as to the notion that another big fat trof digs down into the Ohio Valley by the end of the week.  That is pretty much a very good bet.  That will turn the storm north as the Atlantic ridge just hasn’t had enough time to broaden westward again following the last big trof that dug down and turned Bill.  But, this guy is still a bit sandwiched between a pair of upper lows.  That is lousy for development.  The morning water vapor image sucks.  The Dvorak image is a little better.  Typically, an under developed system may not always follow the flow as decisively as a fully developed storm.  This guy is still gaining tropical characteristics but does have a developing low level circulation.  So, this guy may have more of a westward component initially. than a fully developed storm would.  It will have an opportunity to develop.  Mostl likely it only gets to Cat 1 status because as the trof quickly approaches, it will get into an increasing flow of southwesterly winds ahead of the trof. That will accelerate it northward and eventually north north eastward. It should also mess up any upper level support that it can get.  So, while some models want to make it get stronger than Cat 1, the good environment for that to happen probably won’t be around long enough. 

Tropical Storm Danny Dvorak Image 9:18:45Z 08.26.09

Tropical Storm Danny Dvorak Image 9:18:45Z 08.26.09

Bottom line is that Danny is here.  There is a good chance that it will become a hurricane.  There is a pretty fair chance that it will get deeper as it moves up the east coast.  There is a good chance that it will hit Nova Scotia, perhaps with a greater impact than Bill had.  There is a fair chance that at least the fringes will affect the east coast from the South Carolina/North Carolina border northward and there is something approaching a fair chance that there is a landfall in the US for a time from say the SC/NC border to Wilmington and then perhaps stay inland through Virginia before it re-emerges just offshore.  Lot of variables at this time. 

Tropical Storm Danny Spaghetti Model 12Z 08.26.09

Tropical Storm Danny Spaghetti Model 12Z 08.26.09

Tropical Storm Danny Spaghetti Intensity Model 12Z 08.26.09

Tropical Storm Danny Spaghetti Intensity Model 12Z 08.26.09

Canadian Model Fri Eve-Hurricane Danny Near NC Outer Banks

Canadian Model Fri Eve-Hurricane Danny Near NC Outer Banks

TROPICAL STORM DANNY DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL052009
1100 AM EDT WED AUG 26 2009

SATELLITE IMAGERY SHOWS THAT THE AREA OF DISTURBED WEATHER EAST OF
THE BAHAMAS HAS DEVELOPED A WELL-DEFINED LOW-LEVEL CIRCULATION…
WITH REPORTS FROM A NOAA HURRICANE HUNTER AIRCRAFT INDICATING THE
SYSTEM WAS BEST DEVELOPED BELOW 12000 FT.  QUIKSCAT DATA AND A FEW
OBSERVATIONS FROM THE STEPPED FREQUENCY MICROWAVE RADIOMETER SHOW
TROPICAL STORM-FORCE WINDS OCCURRING NORTH AND NORTHEAST OF THE
CENTER…WHICH IS THE BASIS FOR THE INITIAL INTENSITY OF 40 KT.
THE STORM HAS BEEN TANGLED UP WITH AN UPPER-LEVEL LOW FOR THE PAST
24 HR…AND THE STRUCTURE AS MUCH RESEMBLES A SUBTROPICAL CYCLONE
AS A TROPICAL CYCLONE.  HOWEVER…CYCLONE PHASE ANALYSES FROM
FLORIDA STATE UNIVERSITY SUGGEST THAT DANNY IS MARGINALLY MORE
TROPICAL THAN SUBTROPICAL…HENCE THE DESIGNATION OF TROPICAL
STORM.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/16.  DANNY IS ON THE
NORTH SIDE OF A MID/UPPER-LEVEL LOW CENTERED OVER HISPANIOLA AND
SOUTHWEST OF A MID/UPPER-LEVEL RIDGE CENTER EAST OF BERMUDA.
THIS PATTERN SHOULD STEER DANNY GENERALLY NORTHWESTWARD WITH
DECELERATION FOR THE NEXT 24-36 HR.  AFTER THAT…THE LARGE SCALE
MODELS AGREE THAT A MID/UPPER-LEVEL TROUGH SHOULD DEVELOP OVER THE
GREAT LAKES…WITH A MID/UPPER-LEVEL LOW OVER THE GULF COAST STATES
MOVING EASTWARD OR NORTHEASTWARD.  THIS EVOLUTION SHOULD CAUSE
DANNY TO TURN NORTHWARD AND THEN RECURVE INTO THE WESTERLIES.
WHILE THE MODELS AGREE ON THE SCENARIO…THERE IS ENOUGH SPREAD IN
THE TRACK GUIDANCE TO MAKE IT UNCERTAIN WHAT LAND AREA DANNY MAY
AFFECT.  THE NAM AND THE CANADIAN MODELS FORECAST DANNY TO MAKE
LANDFALL IN EASTERN NORTH CAROLINA IN ABOUT 72 HR AND MOVE UP THE
U. S. EASTERN SEABOARD…WHILE THE GFS…HWRF… AND GFDL SHOW A
MORE EASTERLY TRACK THAT KEEPS DANNY OFFSHORE UNTIL IT REACHES THE
CANADIAN MARITIMES.  THE FORECAST SPLITS THE DIFFERENCE BETWEEN
THESE EXTREMES AND IS A LITTLE TO THE LEFT OF THE MODEL CONSENSUS.
THE FORECAST TRACK IS ROUGHLY PARALLEL TO THE U. S. EAST COAST…AND
ANY DEVIATION FROM THE TRACK COULD MAKE A LARGE DIFFERENCE IN WHAT
AREAS GET IMPACTED BY DANNY.  THEREFORE…IT IS IMPORTANT NOT TO
FOCUS TOO MUCH ON THE EXACT FORECAST TRACK.

THE INTENSITY FORECAST IS PROBLEMATIC.  WATER VAPOR IMAGERY SHOWS
UPPER-LEVEL LOWS NORTH AND SOUTH OF DANNY CONNECTED BY A CYCLONIC
SHEAR AXIS.  THIS IS NOT A IDEAL PATTERN FOR STRENGTHENING…AND
THE LARGE-SCALE MODELS SUGGEST IT MAY TAKE 24-36 HR FOR THE
ENVIRONMENT TO BECOME MORE FAVORABLE.  BASED ON THIS AND THE
CURRENT ORGANIZATION OF THE STORM…THE INTENSITY FORECAST CALLS
FOR SLOW STRENGTHENING FOR THE FIRST 36 HR.  IT THEN SHOWS A FASTER
STRENGTHENING FROM 36-48 HR AS CONDITIONS BECOME MORE FAVORABLE.
AFTER 48 HR…STRONG UPPER-LEVEL SOUTHWESTERLY WINDS ASSOCIATED
WITH THE EASTERN U. S. TROUGHS ARE EXPECTED TO CAUSE INCREASED
SHEAR AND THE BEGINNING OF EXTRATROPICAL TRANSITION.  THE INTENSITY
FORECAST THUS CALLS FOR DANNY TO REACH 65 KT IN 72 HR…THEN BECOME
EXTRATROPICAL BY 96 HR.  THE INTENSITY FORECAST IS IN BEST
AGREEMENT WITH THE SHIPS AND LGEM MODELS.  HOWEVER…IT IS WEAKER
THAN THE FORECASTS OF THE GFDL AND HWRF.

FORECAST POSITIONS AND MAX WINDS

INITIAL      26/1500Z 24.9N  70.3W    40 KT
12HR VT     27/0000Z 25.8N  72.0W    40 KT
24HR VT     27/1200Z 26.8N  73.6W    45 KT
36HR VT     28/0000Z 28.1N  74.5W    50 KT
48HR VT     28/1200Z 30.1N  75.2W    60 KT
72HR VT     29/1200Z 36.0N  73.5W    65 KT
96HR VT     30/1200Z 45.0N  67.0W    65 KT…EXTRATROPICAL
120HR VT     31/1200Z 52.0N  53.0W    60 KT…EXTRATROPICAL

$$
FORECASTER BEVEN

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