211  
WTNT42 KNHC 222043  
TCDAT2  
 
TROPICAL DEPRESSION BETA DISCUSSION NUMBER 21  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL222020  
400 PM CDT TUE SEP 22 2020  
 
HIGH-RESOLUTION VISIBLE SATELLITE IMAGERY, SURFACE OBSERVATIONS, AND  
NOAA DOPPLER WEATHER RADAR DATA FROM SAN ANTONIO AND HOUSTON, TEXAS,  
INDICATE THAT BETA HAS CONTINUED TO WEAKEN. WHAT CONVECTION REMAINS  
IS QUITE SHALLOW WITH A FEW CLOUD TOPS ONLY EXTENDING UP TO 25,000-  
30,000 FT ASL, MAINLY NEAR AND NORTHEAST OF THE CENTER. HOWEVER,  
THOSE LOW-TOPPED SHOWERS ARE QUITE PRODIGIOUS RAIN-PRODUCERS WITH  
RAINFALL TOTALS OF 13-14 INCHES HAVING BEEN MEASURED ACROSS PORTIONS  
OF THE HOUSTON METROPOLITAN AREA THUS FAR. THE INITIAL INTENSITY OF  
25 KT IS BASED ON NEAR-SHORE BUOY AND SURFACE OBSERVING STATIONS.  
 
THE INITIAL MOTION ESTIMATE IS NOW 065/04 KT. A COASTAL CONVERGENCE  
ZONE OR TROUGH HAS FORMED ABOUT 20-25 NMI INLAND FROM THE TEXAS GULF  
COAST AND, OWING TO THE LACK OF ANY SIGNIFICANT DEEP-LAYER STEERING  
FLOW, BETA IS FORECAST TO MOVE SLOWLY ALONG THAT TROUGH AXIS AND  
REMAIN INLAND THROUGHOUT THE FORECAST PERIOD AS A RESULT. THE ECMWF  
AND UKMET MODELS MOVE BETA RAPIDLY NORTHEASTWARD AFTER 48 HOURS, BUT  
THAT SCENARIO SEEMS TO BE OVERDONE GIVEN THE EXPECTED SHALLOW NATURE  
OF THE CYCLONE. THE NEW NHC OFFICIAL TRACK FORECAST IS SIMILAR TO  
THE PREVIOUS ADVISORY TRACK AND LIES CLOSE TO A BLEND OF THE VARIOUS  
CONSENSUS MODELS, EXCEPT THAT I USED THE SLOWER FORWARD SPEED OF THE  
GFS MODEL.  
 
SINCE BETA IS FORECAST TO REMAIN INLAND FOR THE NEXT THROUGHOUT THE  
FORECAST PERIOD, THE CYCLONE IS NOT EXPECTED TO REGAIN TROPICAL  
STORM STATUS. BETA TO DEGENERATE INTO A REMNANT LOW BY 36 HOURS,  
AND DISSIPATE OVER MISSISSIPPI OR ALABAMA IN 96 HOURS, IF NOT  
SOONER. THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS  
ADVISORY AND CLOSELY THE SIMPLE AND CORRECTED-CONSENSUS MODELS IVCN  
AND HCCA.  
 
THIS IS THE LAST NHC ADVISORY ON BETA. FUTURE INFORMATION ON THIS  
SYSTEM, INCLUDING THE RAINFALL THREAT, CAN BE FOUND IN PUBLIC  
ADVISORIES ISSUED BY THE WEATHER PREDICTION CENTER BEGINNING AT  
10 PM CDT, UNDER AWIPS HEADER TCPAT2, WMO HEADER WTNT32 KWNH, AND  
ON THE WEB AT HTTP://WWW.WPC.NCEP.NOAA.GOV  
 
KEY MESSAGES:  
 
1. SIGNIFICANT FLASH AND URBAN FLOODING IS OCCURRING AND WILL  
CONTINUE FOR THE MIDDLE AND UPPER TEXAS COAST TODAY. THE SLOW MOTION  
OF BETA WILL CONTINUE TO PRODUCE A LONG DURATION RAINFALL EVENT FROM  
THE MIDDLE TEXAS COAST TO SOUTHERN LOUISIANA. FLASH, URBAN, AND  
MINOR TO ISOLATED MODERATE RIVER FLOODING IS LIKELY. PERIODS OF  
RAINFALL WILL SPREAD EAST INTO THE LOWER MISSISSIPPI VALLEY,  
PORTIONS OF THE TENNESSEE VALLEY, AND THE SOUTHEAST THROUGH THE END  
OF THE WEEK. FLASH, URBAN, AND ISOLATED MINOR RIVER FLOODING IS  
POSSIBLE ON SMALLER RIVERS.  
 
2. PERSISTENT ONSHORE FLOW WILL CONTINUE TO RESULT IN ABOVE NORMAL  
HIGH TIDES, AND COASTAL FLOODING OVER THE NEXT FEW DAYS WILL BE SLOW  
TO RECEDE. FOR INFORMATION ON THE ONGOING COASTAL FLOODING, PLEASE  
REFER TO COASTAL FLOOD PRODUCTS ISSUED BY LOCAL NATIONAL WEATHER  
SERVICE OFFICES.  
 
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 22/2100Z 29.0N 96.3W 25 KT 30 MPH  
12H 23/0600Z 29.3N 95.6W 25 KT 30 MPH...INLAND  
24H 23/1800Z 30.1N 94.2W 25 KT 30 MPH...INLAND  
36H 24/0600Z 31.3N 92.5W 20 KT 25 MPH...POST-TROP/REMNT LOW  
48H 24/1800Z 32.5N 90.8W 20 KT 25 MPH...POST-TROP/REMNT LOW  
60H 25/0600Z 33.8N 88.9W 20 KT 25 MPH...POST-TROP/REMNT LOW  
72H 25/1800Z 35.1N 87.3W 15 KT 15 MPH...POST-TROP/REMNT LOW  
96H 26/1800Z...DISSIPATED  
 

 
FORECASTER STEWART  
 
 
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