842
WTNT42 KNHC 210841
TCDAT2

Tropical Storm Bertha Discussion Number 8
NWS National Hurricane Center Miami FL AL022026
400 AM CDT Tue Jul 21 2026

Before the Air Force Reserve reconnaissance aircraft departed
Bertha, its final fix indicated the storm was continuing to deepen
with a 998 mb pressure, with peak 700 mb flight-level winds of 46
kt. In addition, an earlier scatterometer pass at 0322 UTC showed a
peak surface wind retrieval of 43 kt on the southern side of the
storm that was not fully sampled by the aircraft. These data
provided the basis to increase Bertha's intensity to 45 kt on the
intermediate advisory. Despite this increase in intensity, TDR data
from the earlier NOAA-P3 mission indicated that Bertha's circulation
remains tilted south with height, and satellite imagery shows the
low-level center now mostly exposed north of the deepest convection
due to increasing vertical wind shear. The initial intensity will
thus remain 45 kt for this advisory.

Tracking the low-level swirl on satellite this morning indicates
that Bertha has resumed a slow northwestward motion at 315/4 kt. The large-scale steering pattern is slowly evolving as a mid-level ridge
currently over the Rockies slides southeastward while a longwave
trough remains over the northeastern United States. This evolution
should result in Bertha moving slowly northwestward or
west-northwestward, turning more westward by the middle of the week. Complicating this track forecast, however, is the expectation that
Bertha will become highly sheared in 24-48 h, and bursts of deep
convection on its southwestern side may try to tug the storm's
center left of the steering motion. The latest NHC track forecast is
slightly north of the previous one for the first 24-36 h, but then
falls back to near the prior forecast track after that time, close
to a blend of the most recent Google DeepMind ensemble mean (GDMI)
and TVCN solutions. It is worth noting that the track forecast
beyond 48 h assumes Bertha is able to maintain its status as a
tropical cyclone, with several models suggesting Bertha could
degenerate into a trough beyond this time period.

Northeasterly vertical wind shear over Bertha is already diagnosed
near 25 kt from UW-CIMSS, and it is forecast to increase further
over the next 24 h. While sea-surface temperatures are plenty warm,
nearby dry air could be imported by this shear into Bertha's center, disrupting its structure. While periodic bursts of deep convection
will likely continue to occur over the next 24-48 h, the latest NHC
intensity forecast only shows a slight additional intensification
today before the shear becomes prohibitively strong. In fact, most
of the guidance suggests Bertha will begin to slowly weaken after 12
h, and the latest NHC intensity forecast now reflects this
reasoning. Once Bertha moves near or over the Gulf coast of
Louisiana, some guidance shows Bertha's circulation becoming
elongated due to the combination of land interaction and high shear
affecting the tropical storm. While the latest NHC forecast still
shows Bertha remaining a tropical cyclone along the Gulf coast
through 72 h, another possibility is that the system degenerates
into a trough as it succumbs to the negative environmental
conditions. The NHC intensity forecast is roughly in the middle of
the guidance envelope.

As mentioned previously, the current shear affecting Bertha is
likely to give the cyclone a very asymmetric structure, with the
bulk of the rainfall and much of the wind expected to occur on the
southern side of the storm center.


Key Messages:

1. Bertha is expected to bring tropical storm conditions to portions
of the Gulf Coast from Alabama westward to southeastern Louisiana
tonight and Wednesday, where a Tropical Storm Warning is in effect.
Tropical storm conditions are possible for portions of the Florida
Panhandle, Metro New Orleans, and the southern Gulf Coast of
Louisiana, where a Tropical Storm Watch is in effect.

2. A Storm Surge Watch is in effect for the Alabama, Mississippi,
and southeastern Louisiana coasts, where a life-threatening storm
surge is possible.

3. Interests elsewhere in Louisiana and Texas should monitor the
progress of this system, as additional watches or warnings could be
required for portions of that area later today.

4. Areas of flash flooding will be possible through Thursday along
the Gulf Coast and adjacent inland locations from the Florida Big
Bend region to southern Louisiana, with isolated instances of flash
flooding possible westward into portions of the Texas coast later in
the week.


FORECAST POSITIONS AND MAX WINDS

INIT 21/0900Z 28.7N 86.4W 45 KT 50 MPH
12H 21/1800Z 29.0N 86.8W 50 KT 60 MPH
24H 22/0600Z 29.4N 87.6W 45 KT 50 MPH
36H 22/1800Z 29.5N 88.7W 40 KT 45 MPH
48H 23/0600Z 29.3N 90.5W 35 KT 40 MPH...INLAND
60H 23/1800Z 29.3N 92.2W 30 KT 35 MPH...OVER WATER
72H 24/0600Z 29.6N 94.2W 30 KT 35 MPH...ON THE COAST
96H 25/0600Z 30.4N 96.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 26/0600Z...DISSIPATED

$$
Forecaster Papin


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