Tropical Storm Cristobal Forecast Discussion Number 24

By | June 7, 2020

Issued at 1000 AM CDT Sun Jun 07 2020


000
WTNT43 KNHC 071450
TCDAT3
 
Tropical Storm Cristobal Discussion Number  24
NWS National Hurricane Center Miami FL       AL032020
1000 AM CDT Sun Jun 07 2020
 
Cristobal's inner-core remains disorganized as multiple low-level 
circulations are seen rotating around the mean center used in the 
advisory. A large swirl just west of the alleged center has been 
dropping southward, and this could become a new center of 
circulation later today. Since the previous advisory, Cristobal's 
overall appearance in satellite imagery has started to look more 
like a tropical cyclone with several small curved convective bands 
developing, especially in the eastern semicircle, along with some 
anticyclonic cirrus outflow noted. NOAA Doppler radar have 
indicated average velocities of 55-58 kt between 5000-8000 ft over 
the Chandeleur Sound, which equates to 45-48 kt surface winds in 
the northeastern quadrant. Also, an earlier Air Force Reserve 
reconnaissance mission sampled a long fetch of 55-59 kt at 925 mb in 
the southeastern quadrant, which equates to 41-44 kt surface winds. 
Therefore, the initial intensity is being held at 45 kt for this 
advisory, which is consistent with satellite intensity estimates of 
45 kt from both TAFB and UW-CIMSS ADT.

The initial motion is an uncertain 355/10 kt due to the uncertainty 
in the center position. Due to the broad inner-core wind field, 
there may be some erratic motion for the next 6 hours or so. 
Otherwise, the models remain in very good agreement in Cristobal 
turning north-northwestward later today. That motion is expected to 
continue until the 36-h period as the cyclone rounds the western 
periphery of a deep-layer ridged parked over the southeastern U.S. 
and Tennessee Valley area. By 48 hours and beyond, the ridge is 
forecast to slide eastward, allowing Cristobal to turn toward the 
north on day 2, and then move northeastward on days 3 and 4. A 
merger with an extratropical cyclone over the Great Lakes area is 
expected by day 5. The new NHC forecast track is similar to the 
previous advisory track, and lies close to the tightly packed 
consensus models.
 
The continued broad structure of Cristobal and significant dry air 
entrainment should prevent any significant intensification before 
landfall, and the current intensity forecast holds the intensity 
constant at 45 kt through 12 h. Although the center is expected to 
be inland at that time, the long southerly wind fetch on the east 
side could keep winds to 45 kt over the Chandeleur Sound, near the 
coast of Mississippi and Alabama, and possibly over the inland 
lakes of southeastern Louisiana. Gradual weakening is forecast after 
landfall, with Cristobal weakening below tropical-storm strength 
by the 24-h time period. The new intensity forecast is similar to 
the previous advisory, and continues to show some slight 
re-intensification after the cyclone becomes extratropical at 
72-96 hours, which is in agreement with the global model guidance.
 
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 should spread along the northern Gulf
coast from central Louisiana to the western Florida Panhandle,
including metropolitan New Orleans today, and a Tropical Storm
Warning is in effect for this area.  These winds will arrive well
in advance of and extend well east of Cristobals center.
 
3. Heavy rainfall will continue across north Florida this morning,
spreading from east to west across the eastern and central Gulf
Coast from the Florida Panhandle into Louisiana today. The Central
Gulf Coast region will be most prone to issues after the passage of
the center of Cristobal from Sunday night into 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  07/1500Z 28.7N  90.0W   45 KT  50 MPH
 12H  08/0000Z 30.2N  90.5W   45 KT  50 MPH...INLAND
 24H  08/1200Z 32.6N  91.6W   30 KT  35 MPH...INLAND
 36H  09/0000Z 35.2N  92.2W   25 KT  30 MPH...INLAND
 48H  09/1200Z 38.9N  91.6W   25 KT  30 MPH...INLAND
 60H  10/0000Z 43.5N  89.6W   25 KT  30 MPH...INLAND
 72H  10/1200Z 47.8N  87.1W   30 KT  35 MPH...POST-TROP/EXTRATROP
 96H  11/1200Z 52.6N  83.1W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  12/1200Z...DISSIPATED
 
$$
Forecaster Stewart
 

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