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Maxwell House on September 18, 2021

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ACUS01 KWNS 181937

SWODY1

SPC AC 181935

Day 1 Convective Outlook

NWS Storm Prediction Center Norman OK

0235 PM CDT Sat Sep 18 2021

Valid 182000Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON

AND EVENING OVER PARTS OF THE GREAT BASIN...

...SUMMARY...

A few storms may produce severe wind and/or hail this afternoon and

evening across parts of the Great Basin region.

...20Z Update...

No changes needed to the previous outlook.

As mentioned in MCD 1767, a few stronger storms remain possible

across the Great Basin this afternoon. Instability has been tempered

by cloud cover and rather limited low-level moisture, but deep

southwesterly flow could still result in a strong wind gusts or two

with any of the more robust storms. Cool mid-level temperatures

could also result in isolated hail, particularly across the higher

terrain.

..Mosier.. 09/18/2021

.PREV DISCUSSION... /ISSUED 1114 AM CDT Sat Sep 18 2021/

...Great Basin...

Water vapor loop shows a strong upper trough digging onto the coast

of OR, with a lead shortwave trough lifting northeastward across

CA/NV toward UT. Large scale forcing is overspreading parts of

NV/AZ/UT, resulting in increasing coverage of thunderstorms. This

activity will spread northeastward across much of UT this afternoon,

and eventually into southern ID/WY. Instability will be limited due

to marginal moisture values and pockets of cloudiness. However,

rather strong southwesterly flow will result in fast-moving showers

and thunderstorms capable of gusty and locally damaging winds. Hail

will also be possible in the higher terrain of northwest AZ into

central UT.

FONT15 KNHC 182034

PWSAT5

POST-TROPICAL CYCLONE ODETTE WIND SPEED PROBABILITIES NUMBER 5

NWS NATIONAL HURRICANE CENTER MIAMI FL AL152021

2100 UTC SAT SEP 18 2021

AT 2100Z THE CENTER OF POST-TROPICAL CYCLONE ODETTE WAS LOCATED NEAR

LATITUDE 39.1 NORTH...LONGITUDE 65.1 WEST WITH MAXIMUM SUSTAINED

WINDS NEAR 40 KTS...45 MPH...75 KM/H.

Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH)

ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME

EASTERN DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME

CENTRAL DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME

WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS

CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST

...34 KT (39 MPH... 63 KM/H)...

...50 KT (58 MPH... 93 KM/H)...

...64 KT (74 MPH...119 KM/H)...

FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS

PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE

OP IS THE PROBABILITY OF THE EVENT BEGINNING DURING

AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY)

(CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN

18Z SAT AND THE FORECAST HOUR (CUMULATIVE PROBABILITY)

PROBABILITIES ARE GIVEN IN PERCENT

X INDICATES PROBABILITIES LESS THAN 1 PERCENT

PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN

THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT.

PROBABILITIES FOR 34...50...64 KT SHOWN WHEN THE 5-DAY

64-KT CUMULATIVE PROBABILITY IS AT LEAST 1 PERCENT.

- - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - -

FROM FROM FROM FROM FROM FROM FROM

TIME 18Z SAT 06Z SUN 18Z SUN 06Z MON 18Z MON 18Z TUE 18Z WED

PERIODS TO TO TO TO TO TO TO

06Z SUN 18Z SUN 06Z MON 18Z MON 18Z TUE 18Z WED 18Z THU

FORECAST HOUR (12) (24) (36) (48) (72) (96) (120)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

LOCATION KT

HIBERNIA OILFD 34 X X( X) X( X) X( X) X( X) 3( 3) 3( 6)

CAPE RACE NFLD 34 X X( X) 4( 4) 2( 6) X( 6) 1( 7) 3(10)

ILE ST PIERRE 34 X 1( 1) 3( 4) X( 4) X( 4) X( 4) 1( 5)

SYDNEY NS 34 X 2( 2) 1( 3) X( 3) X( 3) X( 3) X( 3)

SABLE ISLAND 34 5 23(28) 3(31) X(31) X(31) X(31) X(31)

HALIFAX NS 34 2 1( 3) X( 3) X( 3) X( 3) X( 3) X( 3)

FORECASTER BERGAXNT20 KNHC 182208

TWDAT

Tropical Weather Discussion

NWS National Hurricane Center Miami FL

0005 UTC Sun Sep 19 2021

Tropical Weather Discussion for North America, Central America

Gulf of Mexico, Caribbean Sea, northern sections of South

America, and Atlantic Ocean to the African coast from the

Equator to 31N. The following information is based on satellite

imagery, weather observations, radar and meteorological analysis.

Based on 1800 UTC surface analysis and satellite imagery through

2050 UTC.

...SPECIAL FEATURES...

Post-Tropical Cyclone Odette is centered near 39.1N 65.1W at

18/2100 UTC or 260 nm ESE of Nantucket Massachusetts moving ENE

at 16 kt. Estimated minimum central pressure is 1001 mb. Maximum

sustained wind speed is 40 kt with gusts to 50 kt. The convection

is located well east of the given center with scattered moderate

to strong noted from 35N to 41N between 55W and 63W. Odette

is moving toward the east-northeast and this general motion with

an increase in forward speed is expected through Sun. A turn

toward the east and east-southeast with a decrease in forward

speed is expected on Mon and Tue. On the forecast track, the

center of Odette will pass well south of Atlantic Canada tonight

through Mon. Strengthening as a post-tropical cyclone is forecast

during the next day or two. Please read the latest Atlantic

High Seas Forecast issued by the Ocean Prediction Center at

https://www.ocean.weather.gov/ and the latest NHC Public Advisory

at https://www.nhc.noaa.gov/text/MIATCPAT5.shtml and

Forecast/Advisory at https://www.nhc.noaa.gov/text/MIATCMAT5.shtml

for more details. Please refer to products from the Canadian

Hurricane Centre for additional information on potential impacts

in Newfoundland at weather.gc.ca/hurricane/

Atlantic Gale Warning: A tropical wave is in the Atlantic Ocean

along 51W/52W from 06N to 22N, while a 1008 mb low pressure area

is along the tropical wave near 15.5N52W, or about 650 nm E-SE of

the northern Leeward Islands, moving west at around 15 kt.

Associated winds are currently 20 to 30 kt, and are forecast to

increase to 35 kt in the next few hours with a gale warning

currently in place. Peak seas are currently 8 to 10 ft. Scattered

moderate to strong convection is noted within 300 nm in the east

semicircle, 180 nm southwest quadrant, and 480 nm in the

northwest quadrant. This low continues to show signs of

organization, however satellite-derived wind data from a few hours

ago indicated that the system does not yet have a well- defined

surface circulation. Only a slight increase in organization of

this system would lead to the formation of a tropical depression

or tropical storm, which is expected to occur later today or

tonight while the low moves toward the west-northwest at about 15

kt. This system is expected to be near the northern Leeward

Islands on Mon and Tue, and interests there should monitor its

progress. Upper-level winds are likely to become less conducive

for development when the system reaches the southwestern Atlantic

by the early to middle part of next week. This low has a high

chance for tropical cyclone formation in the next 48 hours.

Additional information on this system, including gale warnings,

can be found in the High Seas Forecasts issued by the National

Weather Service at:

www.hurricanes.gov/marine and latest NHC Tropical Weather Outlook

at www.hurricanes.gov for more details.

A tropical wave is in the Atlantic Ocean along 26W/27W from 03N to

19N, while a 1008 mb low pressure area is along the tropical wave

near 09N26.5W, over the far eastern Atlantic a few hundred nm

south-southwest of the Cabo Verde Islands, moving west at around

5 kt. Associated winds are currently 20 to 30 kt with peak seas of

8 to 10 ft. Scattered moderate to strong convection is noted from

07N to 11N between 25W and 33W. The low continues to show some

signs of organization, and environmental conditions appear

conducive for further development of this system. A tropical

depression could form over the next couple of days while moving

toward the northwest at 10 to 15 kt to the west of the Cabo Verde

Islands. This system is expected to reach cooler waters and an

area of stronger upper- level winds early next week, which could

limit its development. This low has a medium chance for tropical

cyclone formation in the next 48 hours.

Additional information on this system can be found in the Meteo-

France High Seas Forecast at:

http://weather.gmdss.org/II.html and also refer to the latest NHC

Tropical Weather Outlook at www.hurricanes.gov for more details.

...TROPICAL WAVES...

Refer to the Special Features section above for details on two

tropical waves in the Atlantic Ocean.

A tropical wave is located near the Yucatan Peninsula and far

eastern Bay of Campeche along 91W south of 19N into the eastern

Pacific Ocean, moving west at around 10 kt. No deep convection is

occurring in association with this tropical wave over water,

however showers and thunderstorms are noted over northern

Guatemala and portions of eastern Mexico.

...MONSOON TROUGH/ITCZ...

The monsoon trough extends across the coast the Mauritania at

18N16W through 1008 mb low pressure near 09N26.5W to 05N35W to

06N38W. The ITCZ continues from 06N38W to 12N48W. Other than the

convection described above, scattered moderate and isolated strong

convection is noted from 05N to 08N between 33W and 37W. Scattered

moderate convection is noted within 180 nm south of the monsoon

trough and ITCZ between 30W and 46W.

...GULF OF MEXICO...

A surface trough continues to linger over the north-central and

central Gulf from the coast of Louisiana near 29N90W to 24N95W to

22N97W. Scattered moderate and isolated strong convection is noted

within 240 nm southeast of the trough. Another surface trough is

analyzed from 21N95W to 18N94W in the Bay of Campeche. Otherwise,

a broad ridge extends into the eastern Gulf of Mexico. Gentle to

moderate SE-S return flow is noted south of 25N and east of 93W,

with light and variable winds elsewhere. Seas are in the 2 to 4 ft

range across the central and eastern Gulf, and 3 ft or less across

the western Gulf.

For the forecast, weak high pressure will extend across the

eastern and central Gulf of Mexico through early next week. This

pattern will support continued gentle to moderate winds and mostly

slight seas across the Gulf through the next several days.

Looking ahead, a weak cold front may move into the northwest and

north-central Gulf by mid week.

...CARIBBEAN SEA...

The eastern extension of the east Pacific Ocean monsoon trough

enters the SW Caribbean Sea near the Costa Rica and Panama border

and continues to northern Colombia. Scattered moderate to strong

convection is noted south of 11N. Afternoon and early evening

isolated thunderstorms are noted over portions of Hispaniola,

Jamaica and Cuba, as well as portions of Central America.

Otherwise, the rest of the basin is dominated by generally dry

weather conditions, suppressing the development of showers and

thunderstorms. Moderate to fresh trades are noted north of 10N and

west of 80W, with gentle to moderate trades east of 70W. Seas are

6 to 9 ft in the SW Caribbean, 4 to 6 ft elsewhere west of 70W,

and 3 to 5 ft east of 70W.

For the forecast, the Atlantic ridge will shift westward through

Sun. This will support fresh to strong winds over the south-

central Caribbean and Gulf of Honduras into early Sun. The ridge

will weaken starting Sun night as a tropical wave and area of low

pressure currently across the central Atlantic along 52W move to

the northeast of the Leeward Islands early Mon, then begin to move

more northwest. There is a high chance this low pressure will

form into a tropical cyclone over the next several days.

Regardless of further development, expect increase winds, seas and

thunderstorms north through east of the Leewards early next week.

...ATLANTIC OCEAN...

Refer to the Special Features section above for details on two

disturbances in the tropical Atlantic with a chance of tropical

cyclone formation over the next few days.

Otherwise, a broad 1027 mb subtropical ridge anchored near the

Azores extends southwestward to the Bahamas and Florida. A weak

surface trough is analyzed from 30N51W to 23N54W with scattered

moderate convection noted from 23N to 25N between 52W and 56W.

A few showers and thunderstorms are also noted off the northeast

coast of Florida in association with convection spilling from the

Gulf of Mexico. The rest of the basin enjoys fairly tranquil

weather conditions. Fresh to locally strong NE winds are observed

off the coast of northern Africa and the waters surrounding the

Canary Islands. Moderate to fresh trades are noted north of the

convergence zone and east of 40W, with gentle to moderate winds

elsewhere. Seas in the tropical Atlantic east of 55W are in the 4

to 7 ft range, and 3 to 5 ft west of 55W.

For the forecast west of 55W, weak ridging through the northern

Bahamas will support mostly light breezes and slight seas north of

22N through early next week, and moderate to fresh trade winds

and moderate seas south of 22N through Sun. Meanwhile, an area of

low pressure currently over the central tropical Atlantic along

52W will approach the waters northeast of the Leeward Islands Sun

and Mon then begin to move more northwest over open Atlantic

waters. There is a high chance this low pressure will form into a

tropical cyclone over the next several days. Regardless of further

development, expect increase winds, seas and thunderstorms north

through east of the Leewards Islands and northeast of Puerto Rico

early next week.

LewitskyAXNT20 KNHC 182208