754
FXUS02 KWBC 251904
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT FRI AUG 25 2023
VALID 12Z MON AUG 28 2023 - 12Z FRI SEP 01 2023
...THREAT OF A TROPICAL SYSTEM INCREASING FOR THE EASTERN GULF OF
MEXICO REGION MIDWEEK WITH HEAVY RAIN MOSTLY LIKELY ACROSS
FLORIDA...
...HEAT AND HUMIDITY WILL BE CONFINED TO THE GULF COAST REGION
WITH SOME RETURN OF THE HEAT LATE WEEK OVER THE CENTRAL PLAINS...
..OVERVIEW
A GRADUALLY AMPLIFYING UPPER TROUGH WILL LIKELY OVERSPREAD MUCH OF
THE EASTERN HALF OF THE COUNTRY AS NEXT WEEK PROGRESSES. THE
ONGOING EXTREME HEAT AND HUMIDITY OVER THE MID-SECTION OF THE
COUNTRY WILL BE DISPELLED BY A LARGE DOME OF CANADIAN COOL AIR.
AS THE HEAT AND HUMIDITY PERSISTS ACROSS GULF COAST REGION, A
TROPICAL DISTURBANCE OVER THE NORTHWESTERN CARIBBEAN IS FORECAST
TO DRIFT INTO THE EASTERN GULF OF MEXICO NEXT WEEK AND POSSIBLY
TRACK ACROSS FLORIDA MIDWEEK. MEANWHILE, RAIN WILL LIKELY RETURN
TO THE PACIFIC NORTHWEST MIDWEEK NEXT WEEK AS AN UPPER-EVEL LOW
MOVES ONSHORE, WHILE THE NEXT SURGE OF MONSOONAL MOISTURE APPEARS
TO MOVE UP ACROSS THE DESERT SOUTHWEST INTO THE FOUR CORNERS
STATES LATE NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS GENERALLY IN GOOD AGREEMENT WITH THE
SYNOPTIC-SCALE FLOW, FEATURING AMPLIFYING TROUGHING ACROSS THE
EAST FOR THE FIRST HALF OF NEXT WEEK. MEANWHILE, AN UPPER LOW OVER
THE EASTERN PACIFIC ON MONDAY IS FORECAST TO ADVANCE EASTWARD
THROUGH THE PACIFIC NORTHWEST AND INTO NORTH-CENTRAL U.S. THROUGH
THE END OF NEXT WEEK, WITH RIDGING PERSISTING OVER THE SOUTHERN
AND SOUTHWESTERN U.S. MODEL DIFFERENCES APPEAR RELATIVELY MINOR
EVEN OUT TO DAY 7 FOR MUCH OF THE MAINLAND U.S.. THE LARGEST
UNCERTAINTY CONTINUES TO BE RELATED TO WHAT COMES OUT OF THE
TROPICAL SYSTEM OVER THE EASTERN GULF OF MEXICO AND HOW IT
EVENTUALLY INTERACTS WITH THE EASTERN U.S. AMPLIFIED TROUGH. THE
MAJORITY OF THE GUIDANCE TAKES THIS SYSTEM NORTHEASTWARD ACROSS
THE EASTERN GULF EARLY NEXT WEEK, FOLLOWED BY FLORIDA MIDWEEK, AND
OFF THE CAROLINA COASTS THEREAFTER AS THE EAST COAST UPPER TROUGH
RETREATS INTO EASTERN CANADA. THE 12Z GFS TAKES THE SYSTEM ON A
MORE WESTERLY TRACK, PUSHING IT INTO THE INTERIOR SOUTHEAST WHICH
WOULD HELP SEPARATE THE TROPICAL SYSTEM FROM THE EAST COAST UPPER
TROUGH. THIS ALTERNATIVE SCENARIO WOULD RESULT IN A SLOWER-MOVING
TROPICAL SYSTEM TO IMPACT THE SOUTHEAST THROUGH LATE NEXT WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE WORKWEEK BEGINS, A STALLING FRONT WITH MOISTURE POOLING
ALONG IT WILL LIKELY PRODUCE A HEAVY RAINFALL THREAT FROM THE
CENTRAL GULF COAST THROUGH THE SOUTHEAST AND INTO THE
MID-ATLANTIC, REMAINING INTO TUESDAY AND POTENTIALLY SPREADING
INTO THE NORTHEAST TUESDAY AS WELL DEPENDING ON FRONTAL POSITIONS.
A PRIMARY FOCUS IS LIKELY TO BE ACROSS THE CAROLINAS, AND PER
COORDINATION WITH THE LOCAL OFFICES A SLIGHT RISK HAS BEEN ADDED
TO MONDAY'S ERO. DESPITE DRY CONDITIONS OVERALL IN THE PAST FEW
WEEKS THERE, A WET DAY ON DAY 3/SUNDAY WILL LIKELY PRIME THE AREA
TO EXPERIENCE SOME FLASH FLOODING ISSUES. ALSO BY MONDAY AND
ESPECIALLY TUESDAY, THE POSSIBLE TROPICAL SYSTEM IN THE EASTERN
GULF COULD BEGIN BRINGING HEAVY TROPICAL RAINS TO PARTS OF
FLORIDA, FOR A MARGINAL RISK IN SOUTHERN FLORIDA ON MONDAY AND A
SLIGHT RISK FROM THE FLORIDA BIG BEND SOUTHWARD ALONG THE GULF
COAST AS THE FEATURE COULD BE APPROACHING. THE MODERATE SPEED OF
THE SYSTEM COULD LIMIT TOO MUCH FLASH FLOODING, BUT TROPICAL
DOWNPOURS WITH HIGH RAIN RATES SHOULD POSE SOME FLASH FLOODING
THREAT. THE SYSTEM COULD TRACK ACROSS NORTHERN FLORIDA OR SO INTO
THE WESTERN ATLANTIC, WHICH COULD SPREAD HEAVY RAINFALL TO THE
COASTAL CAROLINAS BY WEDNESDAY BUT WITH UNCERTAINTY WITH HOW MUCH
FALLS ONSHORE. STORMS COULD LINGER ACROSS FLORIDA INTO LATE WEEK
WITH A FRONTAL BOUNDARY IN A MOIST ENVIRONMENT.
ABOVE NORMAL MOISTURE IS IN PLACE ACROSS PORTIONS OF THE
CENTRAL/SOUTHERN ROCKIES TO THE FRONT RANGE ON MONDAY, AND
SCATTERED TO WIDESPREAD SHOWERS AND STORMS THAT MAY BE SLOW-MOVING
COULD LEAD TO LOCALIZED FLOODING. A MARGINAL RISK WAS MAINTAINED
IN THIS AREA FOR MONDAY. MUCH OF TEXAS COULD GET SOME WELCOME RAIN
AS WELL NEAR A FRONTAL SYSTEM. SOME CONVECTION MAY REMAIN INTO
TUESDAY WITH LESSER AMOUNTS OVERALL. BY WEDNESDAY MONSOONAL
CONVECTION COULD FOCUS FARTHER WEST LIKELY INTO THE MOGOLLON RIM,
WITH INCREASING COVERAGE ONCE AGAIN BY THURSDAY FOR THE FOUR
CORNERS STATES. IN THE NORTHWEST, THE STRONG UPPER LOW COMING
THROUGH FOR THE FIRST HALF OF THE WEEK WILL PROVIDE SUPPORT FOR
RAINFALL THERE. THERE DOES LOOK TO BE SOME INSTABILITY IN PLACE,
SO LOCALIZED RAIN AMOUNTS/RATES MAY BE HIGH ENOUGH TO CAUSE A FEW
INSTANCES OF FLASH FLOODING.
ANOTHER DAY OF HOT TEMPERATURES AND HIGH HUMIDITY IS POSSIBLE FOR
THE GULF COAST REGION ON MONDAY. ADDITIONAL HIGH MAXIMUM AND
MINIMUM TEMPERATURES ARE LIKELY TO BE SET WHILE HEAT INDICES RISE
WELL ABOVE 110F. FINALLY SOME RELIEF IS IN STORE BY TUESDAY AND
WEDNESDAY WITH NEAR TO JUST ABOVE NORMAL HIGHS EXPECTED, BUT
CONSIDERABLY LOWER HEAT INDICES AS A FRONT OR TWO COME THROUGH.
MEANWHILE HEAT IS FORECAST TO BUILD AGAIN ACROSS THE LOWER
ELEVATIONS OF THE DESERT SOUTHWEST WITH SOME 110S LIKELY ON MONDAY
AND TUESDAY, BUT THIS SHOULD ALSO ABATE SOME BY WEDNESDAY AND
BEYOND. MULTIPLE FRONTS CROSSING THE EAST WILL KEEP TEMPERATURES
SOMEWHAT COOLER THAN AVERAGE THERE FOR MUCH OF NEXT WEEK. THE
CENTRAL U.S. COULD START OFF SOMEWHAT COOLER THAN AVERAGE BUT WITH
A WARMING TREND THROUGH THE WEEK.
KONG/TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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