[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 200240
TCDAT3

Potential Tropical Cyclone Three Discussion Number   2
NWS National Hurricane Center Miami FL       AL032017
1000 PM CDT Mon Jun 19 2017

Earlier this afternoon, an Air Force Reserve reconnaissance
aircraft investigating the central Gulf of Mexico disturbance found
that the multiple swirls that this system possessed had consolidated
into a single low-level circulation center with a pressure of about
1000 mb. However, since the circulation was and still is elongated
north-to-south, the large low pressure system is being maintained as
a potential tropical cyclone for this advisory cycle.

The NWS now has the option to issue advisories, watches, and
warnings for disturbances that are not yet a tropical cyclone, but
which pose the threat of bringing tropical storm or hurricane
conditions to land areas within 48 hours. Under previous policy
this was not possible.  These systems are known as Potential
Tropical Cyclones in advisory products and are numbered from the
same list as depressions. Because of the threat to the central
Gulf coast, advisories have been initiated on Potential Tropical
Cyclone Three and the appropriate watches/warnings have been issued.
Users should be aware that forecast uncertainty for disturbances is
generally larger than for tropical cyclones, especially beyond
48-72 hours.

After stalling this afternoon due to re-organization of the system's
center, the low now appears to be moving 330/07 kt based on recent
conventional and microwave satellite fixes. The new forecast track
has been shifted to the west of the previous advisory track through
48 hours, mainly due to the more westward initial position.
Otherwise, no other significant changes were made to the previous
forecast track. The low is expected to move generally northwestward
through 48 hours around the southwestern portion of a deep-layer
ridge located over the western Atlantic and Florida. After that, the
system is forecast to turn northward around the ridge axis, moving
into the south-central United States. The new NHC track forecast is
a little to the right of the consensus model TVCA. Given the still
disorganized nature of the circulation, and the fact that the wind
and rain hazards extend well north and east of the center, users are
encouraged to not focus on the details of the track forecast.

The initial intensity remains 35 kt based on reconnaissance wind
data and observations from nearby ships 3ETA7 and 3FZO8. Only slight
strengthening is expected for the next 36 hours or so due to
moderate to strong southwesterly vertical wind shear of 25-30 kt.
By 48 hours, the shear is forecast to decrease to 20 kt or less,
but the system will already be close to land at that time and
probably not be able to take advantage of the lower shear
conditions. The NHC intensity forecast is similar to the previous
advisory and the intensity consensus model IVCN.

The primary hazard from this disturbance is expected to be heavy
rainfall over portions of the central and eastern Gulf Coast.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 24.4N  89.5W   35 KT  40 MPH...POTENTIAL TROP CYCLONE
 12H  20/1200Z 25.4N  90.3W   35 KT  40 MPH...TROPICAL CYCLONE
 24H  21/0000Z 26.4N  91.3W   40 KT  45 MPH
 36H  21/1200Z 27.1N  92.1W   40 KT  45 MPH
 48H  22/0000Z 28.3N  92.8W   40 KT  45 MPH
 72H  23/0000Z 31.8N  93.1W   25 KT  30 MPH...INLAND
 96H  24/0000Z 35.2N  90.1W   20 KT  25 MPH...POST-TROP/INLAND
120H  25/0000Z...DISSIPATED INLAND

$$
Forecaster Stewart
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