Prognostic Meteorological Discussion
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FXUS21 KWNC 221958
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 22 2017

SYNOPSIS: A TROPICAL CYCLONE IS LIKELY TO DEVELOP OVER THE SOUTHWESTERN GULF OF
MEXICO PRIOR TO THIS PERIOD AND THEN STRENGTHEN AS IT TRACKS TO THE TEXAS GULF
COAST ON AUGUST 25. A TROPICAL CYCLONE MAY DEVELOP NEAR THE SOUTHEAST COASTLINE
THIS WEEKEND WITH A SUBSEQUENT TRACK TO THE NORTHEAST. UPPER-LEVEL HIGH
PRESSURE IS FORECAST TO BUILD ACROSS THE WESTERN U.S. DURING THE FINAL WEEK OF
AUGUST. UPPER-LEVEL LOW PRESSURE IS LIKELY TO REMAIN CENTERED OVER WESTERN
ALASKA AND THE ALEUTIANS THROUGH WEEK-2.

HAZARDS

HEAVY RAIN FOR THE WESTERN GULF COAST AND INLAND AREAS OF SOUTHEAST TEXAS AND
SOUTHWEST LOUISIANA, FRI-SAT, AUG 25-26.

HEAVY RAIN FOR SOUTHEAST TEXAS, THE LOWER MISSISSIPPI VALLEY, AND THE WESTERN
TO CENTRAL GULF COAST, SUN-TUE, AUG 27-29.

HEAVY RAIN FOR PARTS OF CENTRAL AND SOUTHERN FLORIDA, FRI-SAT, AUG 25-26.

MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE PACIFIC NORTHWEST, NORTHERN
GREAT BASIN, AND NORTHERN ROCKIES, SUN-TUE, AUG 27-29.

HEAVY RAIN FROM THE SOUTHERN KENAI PENINSULA EAST TO THE NORTHERN ALASKA
PANHANDLE, FRI-SAT, AUG 25-26.

HEAVY RAIN FOR PARTS OF SOUTHERN MAINLAND ALASKA, MON-TUE, AUG 28-29.

HIGH RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF EASTERN OREGON AND
WASHINGTON, WED, AUG 30.

MODERATE RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR PARTS OF IDAHO, NEVADA,
OREGON, AND WASHINGTON, WED-FRI, AUG 30-SEP 1.

SLIGHT RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE WESTERN U.S.,
WED-TUE, AUG 30-SEP 5.

FLASH FLOODING POSSIBLE FOR THE DESERT SOUTHWEST, FRI-TUE, SEP 1-5.

FLOODING POSSIBLE FOR PARTS OF THE UPPER MISSISSIPPI RIVER VALLEY.

FLOODING LIKELY FOR PARTS OF KANSAS AND MISSOURI.

SEVERE DROUGHT ACROSS PARTS OF THE GREAT PLAINS, WESTERN CORN BELT, NORTHERN
ROCKIES, AND HAWAII.

DETAILED SUMMARY

FOR FRIDAY AUGUST 25 - TUESDAY AUGUST 29: FORECAST CONFIDENCE CONTINUES TO
INCREASE THAT A TROPICAL CYCLONE FORMS OVER THE SOUTHWESTERN GULF OF MEXICO
PRIOR TO THIS PERIOD. ALTHOUGH THE INTENSITY OF THIS TROPICAL CYCLONE VARIES
AMONG MODEL SOLUTIONS, IT IS EXPECTED TO TRACK NORTHWEST AND MAKE LANDFALL
ALONG THE TEXAS GULF COAST ON AUGUST 25 OR 26. THE REMNANT LOW IS THEN FORECAST
TO REMAIN OVER THE WESTERN GULF COAST OR LOWER MISSISSIPPI VALLEY THROUGH EARLY
NEXT WEEK. THE HEAVY RAIN HAZARD AREAS ARE BASED ON A CONSENSUS BETWEEN THE GFS
AND ECMWF ENSEMBLE MEANS. TOTAL RAINFALL AMOUNTS OF 3 TO 7 INCHES, OR MORE, ARE
LIKELY ACROSS THESE OUTLINED AREAS WITH A FLOODING RISK DURING THIS PERIOD. ON
AUG 25 AND 26, A HIGH WIND HAZARD (SPEEDS GREATER THAN 35 KNOTS) IS POSTED FOR
THE TEXAS GULF COAST DUE TO THE INCREASING CHANCE THAT A TROPICAL CYCLONE MAKES
LANDFALL LATER THIS WEEK. PLEASE REFER TO THE NATIONAL HURRICANE CENTER AND
LOCAL NWS OFFICES FOR THE LATEST FORECASTS.



A TROUGH OF LOW PRESSURE AND ENHANCED MOISTURE ARE EXPECTED TO BRING HEAVY RAIN
(LOCALLY MORE THAN 2 INCHES) TO PARTS OF CENTRAL AND SOUTH FLORIDA ON AUG 25
AND 26. DETERMINISTIC MODEL SOLUTIONS CONTINUE TO INDICATE SLOW TROPICAL
CYCLONE DEVELOPMENT OFFSHORE OF THE SOUTHEAST COASTLINE THIS WEEKEND. THIS WILL
HAVE TO BE CLOSELY MONITORED IN FUTURE OUTLOOKS.



AN UPPER-LEVEL RIDGE IS FORECAST TO STRENGTHEN LATER THIS WEEK ACROSS THE
WESTERN U.S. WITH 500-HPA HEIGHTS INCREASING TO NEAR 588DM. MUCH ABOVE-NORMAL
TEMPERATURES ARE POSTED FOR AREAS OF THE PACIFIC NORTHWEST AND NORTHERN ROCKIES
WHERE MAXIMUM TEMPERATURES ARE FORECAST TO AVERAGE AROUND 12 DEGREES F ABOVE
NORMAL AND EXCEED 90 DEGREES F. ALSO, NUMEROUS WILDFIRES CONTINUE TO BURN IN
THESE SAME AREAS WITH THE LARGEST WILDFIRE (MORE THAN 68,000 ACRES BURNED) AT
NENA SPRINGS IN NORTHERN OREGON.



A DEEP, CLOSED LOW AT 500-HPA IS FORECAST TO DEVELOP OVER THE NORTHERN GULF OF
ALASKA BY THE WEEKEND. THIS CLOSED LOW ALOFT IS EXPECTED TO RESULT IN SURFACE
LOW DEVELOPMENT WITH ONSHORE FLOW BRINGING HEAVY RAIN (MORE THAN 1.5 INCHES PER
24 HOURS) FROM THE SOUTHERN KENAI PENINSULA EAST TO THE NORTHERN ALASKA
PANHANDLE ON AUG 25 AND 26. ANOMALOUS SOUTHERN FLOW WITH A TROPICAL CONNECTION
IS EXPECTED TO AFFECT SOUTHERN MAINLAND ALASKA NEXT WEEK AS A HIGHLY AMPLIFIED
TROUGH (RIDGE) DEVELOPS OVER THE ALEUTIANS (EASTERN ALASKA). THE 0Z
DETERMINISTIC ECMWF MODEL INDICATES A 48-HOUR MAXIMUM OF NEARLY 9 INCHES ON THE
SOUTHERN KENAI PENINSULA ON AUG 28 AND 29.

FOR WEDNESDAY AUGUST 30 - TUESDAY SEPTEMBER 05: A COUPLE OF OUTCOMES EXIST WITH
THE TROPICAL SYSTEM THAT IS LIKELY TO AFFECT THE WESTERN GULF COAST AND LOWER
MISSISSIPPI VALLEY DURING THE DAY 3-7 PERIOD. THE REMNANT LOW MAY LINGER ACROSS
THESE AREAS OR LIFT NORTHEAST TO THE OHIO RIVER VALLEY. ABOVE-NORMAL
PRECIPITATION IS FAVORED FROM THE LOWER MISSISSIPPI TO OHIO VALLEY DURING
WEEK-2, BUT IT IS UNCLEAR WHERE THE HEAVIEST RAIN MAY OCCUR ON DAYS 8 AND 9.



THE GFS, CANADIAN, AND ECMWF ENSEMBLE MEANS ARE MORE AMPLIFIED TODAY WITH THE
UPPER-LEVEL RIDGE OVER THE WESTERN U.S. DURING WEEK-2. THEREFORE, A HIGH RISK
OF MUCH ABOVE-NORMAL TEMPERATURES (60 PERCENT CHANCE OR HIGHER OF MAXIMUM
TEMPERATURES ABOVE THE 85TH PERCENTILE) IS INTRODUCED FOR PARTS OF EASTERN
OREGON AND WASHINGTON ON AUG 30. THE AMPLIFIED RIDGE ALOFT CONTINUES TO SUPPORT
A SLIGHT TO MODERATE RISK OF MUCH ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE
WESTERN U.S.



TROPICAL CYCLONE (TC) DEVELOPMENT IS FAVORED ACROSS THE EAST PACIFIC BY THE
BEGINNING OF WEEK-2. A NORTHWEST TRACK OF A TC CLOSE TO THE BAJA PENINSULA IS
EXPECTED TO BRING A SURGE OF MOISTURE NORTH FROM THE GULF OF CALIFORNIA INTO
THE DESERT SOUTHWEST LATER DURING WEEK-2. THEREFORE, A FLASH FLOODING POSSIBLE
HAZARD IS POSTED FOR THE DESERT SOUTHWEST.



THE U.S. DROUGHT MONITOR VALID ON AUG 15 INDICATES THAT SEVERE TO EXCEPTIONAL
(D2-D4) DROUGHT COVERAGE DECREASED SLIGHTLY FROM 5.38 PERCENT TO 5.33 PERCENT
ACROSS THE CONTINENTAL U.S.

FORECASTER: BRAD PUGH

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