Tropical Depression Joyce Discussion Number 16
NWS National Hurricane Center Miami FL AL102018
1100 AM AST Sun Sep 16 2018
Joyce is barely a tropical cyclone at the moment. The cloud
pattern consists of a low-level swirl with a small patch of deep
convection located about 80 n mi northeast of the center and another
patch of weakening convection well removed from the center in the
northeast quadrant. Visible satellite images and a partial ASCAT
pass indicate that the circulation of the cyclone has also become
increasingly elongated from northeast to southwest. Based on the
system's appearance and the satellite intensity estimates, the
initial wind speed is lowered to 30 kt, making Joyce a tropical
depression.
The depression is moving east-northeastward at 16 kt within the
mid-latitude westerlies, and this motion should continue through
tonight. After that time, the shallow cyclone is expected to slow
down and turn southeastward and then southwestward as it is moves
in the flow on the east side of a building low- to mid-level ridge.
The track models are in fairly good agreement, and little overall
change was made to the previous NHC forecast.
Joyce is currently in a quite hostile environment of 30-40 kt of
west-southwesterly shear. Even though SSTs are relatively warm,
the ongoing strong shear and nearby dry air should continue to cause
the cyclone to gradually weaken. Although the NHC forecast shows
Joyce hanging on as a tropical depression for a couple of more days,
it is very possible that the system could degenerate into a trough
or a remnant low at any time during that period.
Tropical Storm Joyce Discussion Number 8
NWS National Hurricane Center Miami FL AL102018
1100 AM AST Fri Sep 14 2018
Joyce has again changed little in organization since the last
advisory, with several small bands of convection to the east and
northeast of the partly exposed center. The initial intensity
remains 35 kt in agreement with the latest satellite estimates from
TAFB and the CIMSS satellite consensus.
The initial motion is now 180/7. Joyce is currently being steered
by the larger and stronger Helene to its east, and a southward to
southeastward motion is expected for the next 12 h or so. As
Helene passes to the east-northeast of Joyce, Joyce should turn
eastward and northeastward with a faster forward speed due to the
approach of a mid-latitude trough from the west. The global models
have again trended toward a faster northeastward motion after 24 h,
and the NHC track forecast has been adjusted to be faster and a
little farther to the east.
There is no change to the intensity forecast philosophy from the
previous advisory. Southwesterly upper-level winds are forecast to
increase over the cyclone within the next day or two, which should
prevent Joyce from strengthening. The NHC forecast calls for little
change in wind speed over the next 36 h, then shows weakening as the
shear increases further. The global models mostly dissipate Joyce
by day 4, but the system could lose its deep convection and become
post-tropical before that time.
Subtropical Storm Joyce Discussion Number 1
NWS National Hurricane Center Miami FL AL102018
500 PM AST Wed Sep 12 2018
The strong low pressure system which the NHC has been monitoring in
the north Atlantic for a couple of days has developed a cyclonically
curved band of deep convection near the center, and scatterometer
data indicate that the winds are near 40 kt. Since the system is
still vertically stacked with an upper-low, it is then classified
as a subtropical cyclone at this time. However, the cyclone is
gaining organization while it is acquiring tropical characteristics.
The NHC forecast calls for Joyce to transform into a tropical system
in about 12 to 24 hours. Since the ocean is warm, some slight
strengthening is possible during the next 3 days. After that time,
Joyce will be over cooler waters and should then be absorbed by a
larger extratropical low.
Joyce has been moving southwestward or 225 degrees at 5 kt, steered
by the northerly flow around the subtropical high which has been
steering Florence and to west of the mid-latitude trough which
is forcing Helene to recurve. In a couple of days, global models
indicate that the steering pattern will change as the trough
amplifies, and Joyce should then turn toward the northeast with an
increase in forward speed.
2. Satellite images indicate that a strong area of low pressure located
a little more than 600 miles west-southwest of the Azores is rapidly
becoming better organized and a subtropical or tropical storm
appears to be forming. If this trend continues, advisories will be
initiated later today or tonight. The low is forecast to move toward
the southwest for the next couple of days, and then turn to the
northeast behind Hurricane Helene. For more information, see High
Seas Forecasts issued by the National Weather Service.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 5 days...high...90 percent.
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