Tropical Storm CRISTOBAL Advisory 6月8日

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Tropical Storm Cristobal Discussion Number  25
NWS National Hurricane Center Miami FL       AL032020
400 PM CDT Sun Jun 07 2020

At least two low-level vortices have been noted rotating
cyclonically within the broad inner-core circulation, with one swirl
located southeast of the advisory position approaching the
Mississippi Delta and the other swirl located inland to the
northwest of Grand Isle, Louisiana. The larger swirl in the
southeastern quadrant will likely become the dominant low-level
circulation center later tonight after that feature moves inland
and frictional convergence tightens up the broad inner-core wind
field a little bit. The initial intensity remains 45 kt based on
data from surface observations and NOAA Doppler radar velocity data
from Slidell and Mobile, along with a satellite intensity estimate
of T3.0/45 kt from TAFB.

The initial motion estimate is an uncertain 355/06 kt due to the
uncertainty in the center position. Some erratic motion will
still be possible for the next 6-12 hours due to the dumb-belling
motion of the multiple low-level circulations. Overall, however,
the models remain in excellent agreement on Cristobal turning
north-northwestward tonight and continuing that motion through
24 hours. By Monday night, a turn toward north is forecast,
followed by a faster motion toward the northeast on Tuesday and
Wednesday ahead of an approaching frontal system. The cyclone is
expected to slow down on days 3 and 4 during extratropical
transition. The new NHC forecast track is very similar to the
previous track forecast, and lies down the center of the the
tightly packed consensus models.

No significant intensification is expected before landfall occurs
late this afternoon or early evening primarily due to Cristobal's
broad wind field. However, intrusions of dry air could result in
wind gusts of 55-60 kt in some of the stronger squalls. After
landfall, only slow weakening is expected due to the cyclone's large
wind field. In the 60-96 hour period, some slight strengthening to
gale-force strength is forecast due to strong baroclinic forcing
during the extratropical transition, and a long southerly to
south-southwesterly wind fetch blowing across Lake Michigan. The
official intensity closely follows a blend of the GFS, UKMET, and
ECMWF global models.

Cristobal remains a broad and asymmetric storm.  Therefore, one
should not focus on the exact forecast track, since the associated
winds, storm surge, and rainfall extend well away the center.


Key Messages:

1. There is a danger of life-threatening storm surge outside of the
Hurricane and Storm Damage Risk Reduction System from the Mouth of
the Mississippi River to Ocean Springs, Mississippi, and a Storm
Surge Warning is in effect for those areas.  Life-threatening storm
surge remains possible in other portions of southern and
southeastern Louisiana where a Storm Surge Watch is in effect.
Residents in these locations should follow advice given by local
emergency officials.

2. Tropical-storm-force winds will continue to spread along the
northern Gulf coast from central Louisiana to the western Florida
Panhandle, including metropolitan New Orleans this evening, and a
Tropical Storm Warning is in effect for this area.  These winds will
extend well east of Cristobal’s center.

3. Heavy rainfall will continue across north Florida into this
evening, diminishing overnight.  Heavy rain will continue to push
inland across the central Gulf coast this afternoon and into the
Lower Mississippi Valley tonight. The Central Gulf Coast region
will be most prone to heavy rain issues after the passage of the
center of Cristobal from tonight through Monday.  This heavy
rain will move up the Lower and Mid Mississippi Valley Monday into
Tuesday, then across the Upper Mississippi Valley and Northern
Plains Tuesday and Tuesday night.  Flash flooding, and new and
renewed significant river flooding is possible, especially where
heavier rainfall occurs over portions of the Gulf Coast through the
Mississippi Valley.


FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 29.1N  89.9W   45 KT  50 MPH
 12H  08/0600Z 30.9N  90.8W   40 KT  45 MPH...INLAND
 24H  08/1800Z 33.4N  91.6W   25 KT  30 MPH...INLAND
 36H  09/0600Z 36.7N  91.7W   25 KT  30 MPH...INLAND
 48H  09/1800Z 40.5N  90.6W   25 KT  30 MPH...INLAND
 60H  10/0600Z 45.2N  88.3W   30 KT  35 MPH...INLAND
 72H  10/1800Z 48.7N  85.8W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  11/1800Z 53.2N  81.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  12/1800Z...DISSIPATED

$$
Forecaster Stewart