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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
 
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