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Tropical Storm Karl


AlexD

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BULLETIN
TROPICAL DEPRESSION TWELVE ADVISORY NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 AM AST WED SEP 14 2016

...NEW TROPICAL DEPRESSION FORMS OVER THE WESTERN CABO VERDE
ISLANDS...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.0N 25.0W
ABOUT 95 MI...155 KM NW OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1009 MB...29.80 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
At 1100 AM AST (1500 UTC), the center of Tropical Depression Twelve
was located near latitude 17.0 North, longitude 25.0 West. The
depression is moving toward the west-northwest near 14 mph (22 km/h)
and a gradual turn toward the west is expected during the next
couple of days.  On the forecast track, the center of the depression
should move through the western islands of Cabo Verde this
afternoon and move away from the islands tonight.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Slight strengthening is expected during the next 24 hours, and the
depression could become a tropical storm tonight.  After that time,
some weakening could occur as the cyclone encounters unfavorable
upper-level winds.

The estimated minimum central pressure is 1009 mb (29.80 inches).


HAZARDS AFFECTING LAND
----------------------
WIND: Gusty winds are possible over portions of the Cabo Verde
Islands through tonight.

RAINFALL: Locally heavy rains are expected over portions of the Cabo
Verde Islands through Thursday. [/quote]

 

 
 

 

TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
1100 AM AST WED SEP 14 2016

Satellite imagery, scatterometer data, and surface observations
indicate that the low pressure area over the Cabo Verde Islands has
developed a well-defined circulation and sufficient organized
convection to be considered a tropical depression.  The initial
intensity is set at 30 kt based on the scatterometer data along
with satellite intensity estimates from TAFB and SAB.

The initial motion is 300/12.  A low- to mid-level ridge should
steer the system west-northwestward and then westward during the
forecast period, with some decrease in forward speed after 36 hours
as the ridge weakens slightly.  The forecast track is near the
center of the guidance envelope and close to the various consensus
models.

Some strengthening is expected during the next 12-24 hours.  After
that, the cyclone is likely to encounter strong westerly vertical
wind shear while over sea surface temperatures of about 26C.  This
combination should lead to weakening, and the intensity forecast
shows the system weakening back to a depression by 36 hours.  Near
the end of the forecast period, the dynamical models diverge on the
evolution of the upper-level winds, with the ECMWF and UKMET
forecasting a more favorable pattern than the GFS. Based on this,
the forecast shows some re-intensification by 120 hours.  An
alternative scenario is that the cyclone degenerates to a tropical
wave as forecast by the GFS.  Overall, the intensity forecast is on
the low side of the guidance in best agreement with the LGEM.

Locally heavy rains and gusty winds are possible over the Cabo
Verde Islands.  However, current indications are that the cyclone
will not reach tropical-storm strength until it has moved west of
the islands.  Therefore, watches and warnings are not required at
this time.


FORECAST POSITIONS AND MAX WINDS

INIT  14/1500Z 17.0N  25.0W   30 KT  35 MPH
 12H  15/0000Z 17.5N  26.8W   35 KT  40 MPH
 24H  15/1200Z 17.9N  29.3W   35 KT  40 MPH
 36H  16/0000Z 17.9N  31.7W   30 KT  35 MPH
 48H  16/1200Z 17.8N  34.0W   30 KT  35 MPH
 72H  17/1200Z 17.5N  38.0W   30 KT  35 MPH
 96H  18/1200Z 17.5N  41.5W   35 KT  40 MPH
120H  19/1200Z 18.0N  45.5W   40 KT  45 MPH

$$ [/quote]

 

145138W5_NL_sm.gif

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The 12z model suites show a variety different solutions in the longer range, all of which are viable possibilities, and validate that TD Twelve needs to be watched.

The GFS just seems to fail to develop Twelve any more than it already has, and opens the wave back up when it nears the Carribean, making it the weakest solution. Interestingly, the GFS track seems to be further south of most of the other model runs as well, which probably has some impact on how well the storm develops.

The GFS seems to be an outlier in terms of not strengthening the storm any. All other model runs seem to show development begin to occur as Twelve moves into the Carribean. The main question at this point is that where- if at all- will Twelve slip through a crack in the block to its north? The CMC seems to do this early on, as the storm is over the eastern Carribean. After reviewing the model run, it seems to do this as a result of it strengthinging Julia as it's stalled off the coast, weakening the ridge. The NAVGEM and ECMWF models both seem to be in agreement on this not happening until later, however. The ECMWF, especially, seems to take this storm and develop it rapidly, as it approaches the US coast. It's not entirely clear to me if the ECMWF solution would end up as a landfall, however it would certainly be a close call if this solution were to occur. Certainly, it seems to me that we shouldn't just shrug Twelve off as a fish storm yet.

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15 hours ago, RubiksDestroyer said:

The 12z model suites show a variety different solutions in the longer range, all of which are viable possibilities, and validate that TD Twelve needs to be watched.

The GFS just seems to fail to develop Twelve any more than it already has, and opens the wave back up when it nears the Carribean, making it the weakest solution. Interestingly, the GFS track seems to be further south of most of the other model runs as well, which probably has some impact on how well the storm develops.

The GFS seems to be an outlier in terms of not strengthening the storm any. All other model runs seem to show development begin to occur as Twelve moves into the Carribean. The main question at this point is that where- if at all- will Twelve slip through a crack in the block to its north? The CMC seems to do this early on, as the storm is over the eastern Carribean. After reviewing the model run, it seems to do this as a result of it strengthinging Julia as it's stalled off the coast, weakening the ridge. The NAVGEM and ECMWF models both seem to be in agreement on this not happening until later, however. The ECMWF, especially, seems to take this storm and develop it rapidly, as it approaches the US coast. It's not entirely clear to me if the ECMWF solution would end up as a landfall, however it would certainly be a close call if this solution were to occur. Certainly, it seems to me that we shouldn't just shrug Twelve off as a fish storm yet.

Looks like the GFS caught onto the idea of developing into something more than an open wave as of 00z runs. Both the ECMWF and GFS look to be in a general consensus that it will start heading more NNW and track near Bermuda before taking on a NE trajectory. This would tend to be in agreement with some of the other tropical models.

http://my.sfwmd.gov/sfwmd/common/images/weather/plots/storm_12.gif

http://www.tropicaltidbits.com/storminfo/12L_tracks_latest.png

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Not the best news for those hoping for an East Coast landfall:

000
WTNT42 KNHC 162046
TCDAT2

TROPICAL STORM KARL DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016
500 PM AST FRI SEP 16 2016

Convection is quite strong in the northeastward quadrant of Karl,
although the center has recently become exposed due to
moderate-to-strong westerly shear.  There has been little
change to the overall satellite presentation in the past several
hours, and the initial wind speed is kept at 40 kt.  A continuation
of the shear is forecast to keep Karl from strengthening much over
the next day or two. This shear is forecast to relax by all of the
models by early next week, and some strengthening should then take
place while Karl moves over warmer waters.  The amount of
intensification is a big question mark, with the GFS/ECMWF now
showing only a weaker tropical storm, while the rest of the standard
intensity guidance (HWRF, GFDL, SHIPS and LGEM models) have Karl as
a hurricane by the end of the period.  Because of the uncertainty,
the intensity forecast is kept the same as the previous one, not too
far from the model consensus.

The initial motion estimate is about the same as before, 280/12.
Model guidance has made a large northward shift today due to the
forecasted interaction of a mid/upper-level trough with Karl over
the next few days.  Initially, the tropical cyclone was expected to
be on the western side of the trough, which would have helped steer
the cyclone more to the west-southwest over the next couple of
days.  However, almost all of the guidance now show the trough
staying to the west of Karl, which would impart a west or
west-northwest motion during that time.  The lack of a
west-southwest track has large implications down the line, with the
cyclone gaining a lot more latitude since Karl is closer to a
weakness in the subtropical ridge.  Continuity dictates that the
NHC forecast not be shifted as much as the guidance suggests for
this package, since the guidance could still shift back to the
south.  A large northward adjustment is made to the NHC forecast at
all times, but it remains south of the model consensus and the
ECMWF solutions.


FORECAST POSITIONS AND MAX WINDS

INIT  16/2100Z 18.8N  35.6W   40 KT  45 MPH
 12H  17/0600Z 19.0N  37.3W   40 KT  45 MPH
 24H  17/1800Z 19.0N  39.7W   40 KT  45 MPH
 36H  18/0600Z 19.0N  42.5W   40 KT  45 MPH
 48H  18/1800Z 19.0N  45.3W   45 KT  50 MPH
 72H  19/1800Z 20.0N  50.5W   50 KT  60 MPH
 96H  20/1800Z 22.0N  55.5W   60 KT  70 MPH
120H  21/1800Z 25.0N  60.5W   70 KT  80 MPH

$$
Forecaster Blake
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