Issued at 400 AM CDT Tue Jul 21 2026
000 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
