Tropical Storm Isaias moved up the east coast, passing through southern Maryland on the morning of Tuesday, August 4th, 2020, spawning several tornadoes as well as flooding rain and tropical storm force winds. Storm total rainfall ranged from 2 to 4 inches near Interstate 95 to as much as 9 inches in Calvert County east of Interstate 95.
Every event with a place to put it; 9 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS LWX wrote it up.
Tropical Storm Isaias moved up the east coast, passing through southern Maryland on the morning of Tuesday, August 4th, 2020, spawning several tornadoes as well as flooding rain and tropical storm force winds.
Storm total rainfall ranged from 2 to 4 inches near Interstate 95 to as much as 9 inches in Calvert County east of Interstate 95. The heavy rain led to numerous incidents of flooding and flash flooding, especially near and east of Interstate 95.
The highest sustained wind of 46 knots was reported at Bishops Head and the highest peak gust of 63 knots was also reported at Bishops Head.
There were three tornadoes associated with Isaias over southern Maryland and there were also numerous reports of downed trees from tropical storm force winds, especially near and east of Interstate 95.
A storm surge of 1 to 2 feet occurred along the western shore of the Chesapeake Bay and the shore of the Tidal Potomac River. This did result in minor tidal Flooding in Washington DC.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Baltimore/Washington wrote its last area forecast discussion before the first event at Aug 4, 3:07 AM EST, 1 hour 53 minutes earlier.
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
407 AM EDT Tue Aug 4 2020
.SYNOPSIS...
Tropical Storm Isaias will pass northeastward over the
Chesapeake Bay today. Refer to the National Hurricane Center for
the latest regarding the track of Isaias. A weak frontal
boundary will linger near the area for the middle and latter
portion of the week.
&&
.NEAR TERM /THROUGH TONIGHT/...
Main story is over the next 6-12 hours as Isaias passes
northward up the East Coast. Right now the center looks to track
near our southern Maryland zones later this morning as it moves
up the Chesapeake Bay. Forecast was not significantly altered,
with winds gusting to tropical storm force back to I-95 and
sustained near the bay. Thus, tropical storm warnings were not
changed. Winds will only start to increase near dawn from south
to north, with strongest winds near and just after the center
passes. With guidance now firmly keeping the heavy rain east of
the Blue Ridge, the flash flood watch was cut back in the west,
and may need more trimming. Still expect heaviest rain to fall
near or just east of I-95 corridor, just west of the center
track. Near and just east of the center track, a tornado threat
remains, and a tornado watch is out until noon. By later this
afternoon, 2 or 3 PM, the system looks likely to have cleared
our region with partial clearing and a gusty northwest wind.
Some stray instability showers may develop on the back side, but
overall, a much nicer afternoon than morning with highs in the
80s. Quiet weather should ensue behind the system tonight,
with stray storms dissipating. Lows in the 60s to low 70s.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
A frontal boundary will shift southeastward across the region on
Wednesday before making its way back northwest on Thursday. This
will keep temps closer to normal for a change. However, the
front being nearby will result in spotty showers and t-storms.
These will be most likely in our southern zones Wednesday, but
may become more widespread further north on Thursday.
&&
.LONG TERM /FRIDAY THROUGH MONDAY/...
Low pressure will track along a stalled frontal boundary to our
southeast on Friday as an upper trough axis and associated
shortwave energy lifts across our north. Showers and
thunderstorms are expected as a result, with the potential for
localized flooding given the antecedent wet conditions in place.
Depending on the timing of the shortwave, rain chances may
linger into the overnight hours. The trough looks to push
through our region on Saturday, helping kick the boundary to our
southeast off the coast. Will carry a low end chance of
showers/storms Saturday should the aforementioned trough take
its time exiting the area. Drier conditions look to take hold
the second half of the weekend and into early next week as high
pressure as the surface and aloft builds into the region. There
may be some diurnally driven showers and storms over the higher
terrain, so won't be advertising a POP free forecast, but most
locations likely remain on the dry side. Temperatures will stay
on the cooler side of climo through the weekend as we reside
north of the stalled boundary, with highs in the 80s each day,
slowly moderating into early next week, while overnight lows
fall back into the 60s.
&&
.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
Isaias is the main story as IFR cigs/vsby with widespread
showers and isolated thunderstorms this morning should lift
northeast later this afternoon, with VFR returning. Winds
increase with gusts potentially 30-40 knots as the center passes
late this morning and midday. After that, an isolated storm
could cause a brief reduction in conditions later this
afternoon, and again at various times over the following couple
of days, but VFR with much lighter winds should prevail.
Potential for episodes of sub VFR conditions will be possible
on Friday as a stalled frontal boundary lingers southeast of the
terminals and upper disturbance nears, sparking showers and
thunderstorms. VFR on Saturday with lower rain chances and
decreasing threat for sub VFR conditions. Winds will
&&
.MARINE...
Tropical Storm Warnings remain in effect through today as Isaias
passes northward across the region. Strongest winds will be over
the middle bay and lower Potomac, but gusts above 40 knots
possible all the way up the Potomac and to the north end of the
bay. Much lighter winds with limited if any weather issues other
tha isolated t-storms Wednesday and Thursday.
Light east northeast winds will prevail over the marine
district Friday through Saturday as a stalled boundary resides
to our southeast. Afternoon/evening showers and thunderstorms
could yield a gusty wind threat on Friday, potentially requiring
the need for Special Marine Warnings.
&&
.HYDROLOGY...
Isaias will be the main story with widespread heavy rainfall
this morning, ending this afternoon. With a better consensus of
the heaviest rain staying east of the Blue Ridge, watch was
dropped to the west. Heaviest rain still looks to be along I-95
or just east with 3-6 inches widespread. Caveat of note is that
the rapid movement of the system could help limit the storm
totals a bit, but still too uncertain on this. River flooding
may persist for a day or two after this if enough rain gets into
the mainstem basins.
&&
.TIDES/COASTAL FLOODING...
Coastal flood warnings remain in effect for the western shore
of the Chesapeake Bay and Washington Southwest Waterfront
through tonight. Coastal flood advisories are in effect for the
remaining tidal coastline. Latest guidance continues the
reduced risk for a large prestorm surge, focusing more on the
latter half of the event. It is important to note that shoreline
facing the open bay will likely have higher water levels than
more protected areas (such as the gauges at Solomons and Straits
Point). Also, due to the nature of the surge, the highest water
levels may not occur at the normal high tide times. Please
reference the latest CFW product or AHPS for more details.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Tropical Storm Warning for DCZ001.
Flash Flood Watch through this evening for DCZ001.
Coastal Flood Warning from 3 PM this afternoon to 3 AM EDT
Wednesday for DCZ001.
MD...Tropical Storm Warning for MDZ005-006-011-013-014-016>018-
503>508.
Flash Flood Watch through this evening for MDZ003>006-011-013-
014-016>018-503>508.
Coastal Flood Advisory from 11 AM this morning to 3 AM EDT
Wednesday for MDZ016.
Coastal Flood Warning from 11 AM this morning to 3 AM EDT
Wednesday for MDZ011-014-017-018.
Coastal Flood Warning from 1 PM this afternoon to 3 AM EDT
Wednesday for MDZ508.
Coastal Flood Advisory from 3 PM this afternoon to 3 AM EDT
Wednesday for MDZ013.
VA...Flash Flood Watch through this evening for VAZ036>040-050-051-
056-507-508.
Tropical Storm Warning for VAZ052>057.
Flash Flood Watch through this evening for VAZ031-052>055-057-
501-502-505-506.
Coastal Flood Advisory from 11 AM this morning to 3 AM EDT
Wednesday for VAZ052-055-057.
Coastal Flood Advisory from 3 PM this afternoon to 3 AM EDT
Wednesday for VAZ053-054.
WV...Flash Flood Watch through this evening for WVZ053.
MARINE...Tropical Storm Warning for ANZ530>543.
&&
SYNOPSIS...BKF/RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...BKF
AVIATION...BKF/RCM
MARINE...BKF/RCM
HYDROLOGY...RCM
TIDES/COASTAL FLOODING...RCMHazardous Weather Outlook National Weather Service Baltimore MD/Washington DC 509 AM EDT Tue Aug 4 2020 ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-050915- Chesapeake Bay north of Pooles Island MD- Chesapeake Bay from Pooles Island to Sandy Point MD- Chesapeake Bay from Sandy Point to North Beach MD- Chesapeake Bay from North Beach to Drum Point MD- Chesapeake Bay from Drum Point MD to Smith Point VA- Tidal Potomac from Key Bridge to Indian Head MD- Tidal Potomac from Indian Head to Cobb Island MD- Tidal Potomac from Cobb Island MD to Smith Point VA- Patapsco River including Baltimore Harbor- Chester River to Queenstown MD-Eastern Bay- Choptank River to Cambridge MD and the Little Choptank River- Patuxent River to Broomes Island MD- Tangier Sound and the inland waters surrounding Bloodsworth Island-District of Columbia-Southern Baltimore-Prince Georges- Anne Arundel-Charles-St. Marys-Calvert-Southeast Harford- Prince William/Manassas/Manassas Park-Fairfax- Arlington/Falls Church/Alexandria-Stafford-Spotsylvania- King George- 509 AM EDT Tue Aug 4 2020 This Hazardous Weather Outlook is for the Maryland portion of the Chesapeake Bay, Tidal Potomac River, and adjacent counties in central Maryland and northern Virginia as well as the District of Columbia. .DAY ONE...Today and Tonight A Tropical Storm Warning is in effect for the entire outlook area today as Tropical Cyclone Isaias moves over the area. A Flash Flood Watch and Coastal Flood Warnings are also in effect today into tonight. Refer to the Flash Flood and Coastal Flood messages for more details. A Tornado Watch is also in effect for the counties in Maryland along the western shore of the Chesapeake Bay until noon. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Scattered thunderstorms may produce isolated instances of flooding Wednesday and Thursday. .SPOTTER INFORMATION STATEMENT... Please report any instances of flooding or wind damage to the National Weather Service. MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053- 055-501>506-050915- Washington-Frederick MD-Carroll-Northern Baltimore- Extreme Western Allegany-Central and Eastern Allegany- Northwest Montgomery-Central and Southeast Montgomery- Northwest Howard-Central and Southeast Howard-Northwest Harford- Augusta-Rockingham-Shenandoah-Frederick VA-Page-Warren-Clarke- Nelson-Albemarle-Greene-Madison-Rappahannock-Orange-Culpeper- Northern Fauquier-Southern Fauquier-Western Highland- Eastern Highland-Western Loudoun-Eastern Loudoun- Northern Virginia Blue Ridge-Central Virginia Blue Ridge- Hampshire-Morgan-Berkeley-Jefferson-Hardy-Western Grant- Eastern Grant-Western Mineral-Eastern Mineral-Western Pendleton- Eastern Pendleton- 509 AM EDT Tue Aug 4 2020 This Hazardous Weather Outlook is for eastern West Virginia, northern and central Virginia, and central and western Maryland with the exception of Garrett County. .DAY ONE...Today and Tonight A Tropical Storm Watch is in effect for portions of central Maryland today as Tropical Cyclone Isaias moves over the area. A Flash Flood Watch is in effect for portions of the outlook area, primarily along and east of the Blue Ridge, today into tonight. Refer to the Flash Flood message for more details. A Tornado Watch is also in effect for the counties in Maryland along the western shore of the Chesapeake Bay until noon. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Scattered thunderstorms may produce isolated instances of flooding Wednesday and Thursday. .SPOTTER INFORMATION STATEMENT... Please report any instances of flooding or wind damage to the National Weather Service.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1258 AM EDT TUE AUG 04 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0415 PM TSTM WND DMG 1 N BRANDYWINE 38.72N 76.85W
08/03/2020 PRINCE GEORGES MD DEPT OF HIGHWAYS
TREE DOWN ON US-301 CRAIN HGWY AT DYSON RD
&&
EVENT NUMBER LWX2001837
SMZThe Sterling radar (KLWX), 79 km away, was scanning. The volume nearest the first event began at 10:28 UTC.
18 flash flood, 13 flood, 9 tropical storm, 4 tornado. Local standard time, as filed.
Sustained winds of 39 mph reported at the U.S. Naval Academy ASOS (KNAK) at 7:56 AM EST, with a peak wind gust of 56 mph at 8:07 AM EST. Isolated reports of trees down across the county, but no significant damage reported.
Tropical Storm Force winds observed at Patuxent River Naval Air Station ASOS (KNHK) with sustained winds of 40 mph at 8:04 AM EST, and a peak wind gust of 58 mph at 9:12 AM EST. Also observed at St. Indigoes MD ASOS (KNUI) with sustained winds of 30 mph at 7:53 AM EST, and a peak wind gust of 52 mph at 8:35 AM EST. Dozens of reports of trees down in a few areas as a result of these winds, one of which fell onto a vehicle in motion, killing the motorist. There was also an EF-0 tornado near Scotland, MD and an EF-1 tornado near Piney Point, MD.
Dozens of trees reported down countywide from tropical storm force wind gusts. An EF-1 tornado also occurred near Plum Point, and another near Solomons.
Sustained winds of 31 mph reported at the Andrews Air Force Base ASOS (KADW) at 8:03 AM EST, with a peak wind gust of 44 mph at 8:19 AM EST. Isolated reports of trees down across the county, but no significant damage reported.
Isolated reports of trees down across the county, but no significant damage reported.
The Howard County 911 Center received about a dozen calls for trees, branches, and wires down.
The Howard County 911 Center received about a dozen calls for trees, branches, and wires down.
Numerous trees were down throughout southeastern Montgomery County. There was an injury due to a tree down on an occupied vehicle near the intersection of West Lake Drive and Tuckerman Lane.
A tropical storm force wind gust of 36 knots was reported near Hickory.
At 6:27 AM EDT, a tornado rated EF-0 caused damage near Scotland, MD.|The survey found tree damage along a portion of Point Lookout|Road between St. Gabriels Manor Way and Fresh Pond Neck Road.|First evidence of tornado touchdown was near the intersection of|St. Gabriels Manor Way and Route 5/Point Lookout Rd where numerous|tree limbs were down.
As the tornado moved north-northwest, numerous trees were snapped|or downed all along the 12800 block of Point Lookout Rd. An|entire row of cedar trees was pushed over behind one residence. A|resident who was home when the tornado passed over stated they|heard a violent roaring sound, the house visibly shook, and then|it was over in a matter of seconds. A row of trees behind the|residence was uprooted during this time.
The tornado lifted shortly before crossing Fresh Pond Neck Road at|Point Lookout Rd and then touched down further north near the|intersection of Curleys Rd and Point Lookout Rd knocking down a|tree on Curleys Rd. The tornado finally knocked down a tree on a|farm just northeast of the aforementioned intersection before|lifting at 6:31 AM EDT.
At 6:32 AM EDT, a tornado rated EF-1 formed soon after the storm|moved northwest of Piney Point, MD. Consistent tree damage began|along Piney Point Road between Tall Timbers and Valley Lee. An|aerial survey was conducted, and a path of snapped and uprooted|trees about 75 to 100 yards wide was noted extending to the|northwest through the woods and fields of rural St. Marys|County. Some roads having multiple trees downed along this path|included Blake Creek Road, Richey Road, and Medleys Neck Road.|Homes were damaged by falling trees, including one along Medleys|Neck Road near the intersection with Scarlet Tanager Way.
The tornado crossed Route 5/Point Lookout Road near the|intersection with Lightfoot Way. Here there was also significant|tree damage. Large trees were uprooted damaging a shed and a home.|A mobile home/camper was blown over on its side. The tornado then|dissipated at 6:41 AM EDT.
The river gage on the St. Marys River near Great Mills, MD exceeded the 6 foot flood stage during the indicated period. Widespread flooding occurred in Great Mills, with water approaching homes and businesses. The peak level of 11.57 feet occurred at 10:15 AM.
One of four confirmed tornadoes spawned by Tropical Storm Isaias|over lower southern Maryland touched down along Point Patience Drive|between the Navy Recreation Center Solomons Fishing Pier and Third|Cove. The tornado tracked northeastward roughly along Patuxent|Drive, uprooting and snapping numerous trees along its path. The|trees fell in a convergent manner over a path of nearly one mile|long and about 175 yards wide, indicating a tornadic circulation was|in contact with the ground. Two recreational vehicles on the Navy|facility were smashed by falling trees. Fortunately there were no|occupants at the time. Trees fell on numerous recreational|facilities on the compound, and damage was noted to outdoor|umbrellas at the pool which were rated for hurricane force winds.|NWS 88D Doppler Radar, as well as the FAA Terminal Doppler Weather Radars|TDCA and TADW all indicated strong rotation over this area.
The tornadic damage ended near the north end of the Naval facility,|and no damage was noted in the adjacent residential community to the|north. Many other scattered trees were knocked down all across|Calvert County and lower southern Maryland due to winds associated|with Tropical Storm Isaias.
Maryland Route 5 was flooded and closed at the Intersection of Route 246 at the St. Marys River.
At 7:33 AM EDT, an EF-1 tornado came onshore at Plum|Point near Beach Drive approximately 5 miles east of Huntingtown,|MD. The tornado moved west along Shore Drive, uprooting numerous|trees and snapping and twisting others. A large tree halfway|along Shore Drive fell on a house, causing structural damage. The|tornado proceeded to move to the end of Shore Drive and shifted|southwest along Ridge Road causing trees to snap about 20 feet up|and fall in multiple directions. Some trees that were snapped were|a foot and a half in diameter.
The tornado then moved across Plum Point Creek and the grassy wetlands|toward Tobacco Road. A swath of trees had their tops broken off east of|Tobacco Road and fell mainly in a south to west direction.
The tornado then proceeded up Tobacco Road near Tobacco Lane, and|moved northward towards Breezy Point Road. Peak winds in the tornado|were estimated to have reached 90 mph here. Over 30 trees were|uprooted, and some were broken in half. A house had a tree fall on|it along the Tobacco Road area, and windows were blown in on another|house. Tobacco Road had over 10 trees fall westward over the road|along with multiple power poles. A 75 to 100 yard path of tree|damage was observed east of Tobacco Road with trees falling in|multiple directions. The area of Tobacco Road from Pinewood Terrace|to Tobacco Lane became impassable due to the tree and power line|damage, and the Breezy Point area became cut off from the main road.
The tornado moved west after passing Breezy Point Road and caused|numerous trees to fall along Route 261/Bayside Road near Bristol|Drive. A large tree near the intersection of Route 261 and Bristol|Drive fell on a house. The tree damage path was observed up to|50 to 75 feet down the north end of Bristol Drive.
The tornado then crossed MD-261, downing more trees and tearing siding from homes near the intersection of Holbrook Lane and Pleasant Court. One tree fell into a house, knocking out a window. No further tornadic damage was observed beyond this point.
Flowing water covered Mechanicsville Road near Beverly Drive.
Maryland Route 5 was closed due to high water at Moll Dyers Run.
The water level rapidly rose above flood stage along the St. Clement Creek in Clements. The water level crested at 9.09 feet at 10:00 AM on August 4th. Water approached Route 234 and 242. Water also approached homes near the creek north of Clements.
Maryland Route 242 was closed due to high water at Locust Run prior to Doctor Johnson Road.
Maryland Route 234 was closed just west of Chaptico at Chaptico Creek.
Maryland Route 242 was closed due to high water at Oakley Road.
MD-6 New Market Turner Road was washed away over Persimmon Creek.
Maryland Route 243 was closed due to high water at Nelson Run near Leonardtown.
Maryland Route 4 was closed at Glebe Run near Brown Road due to high water.
Maryland Route 381 was closed at Swanson Creek due to high water. There were water rescues reported with two vehicles and at least two occupants.
Northbound Kenilworth Ave. closed due to high water at Rottenhouse St.
The water rapidly rose above flood stage along the Whitemarsh Run in Whitemarsh. The water crested at 13.02 feet at 10:25 AM EST on August 4th. The Town Center Court was flooded.
Maryland Route 5 was close due to high water at McIntosh Run near Leonardtown.
Water was flowing across north Ryceville Road.
The water level rapidly rose above flood stage along the Otter Point Creek at Edgewood. The water level crested at 8.67 feet at 10:01 AM August 4th. Winter Run Road was flooded near Singer Road.
Maryland Route 695 was closed due to high water near Belclare Road.
A water rescue was reported on Budds Creek Road in Clements.
Maryland Route 7 was closed near Mohrs Lane due to high water.
MD-262 closed due to flooding of Chew Creek.
MD 263 at Hunting Creek was closed due to high water.
MD 765 was closed at Parkers Creek Road due to high water.
Several portions of Route 4 were closed due to high water.
Beech Dr. closed due to flooding along Rock Creek.
MD-214 closed due to flooding near Beards Creek.
Furnace Ave. closed due to flooding at the Howard/Anne Arundel County line.
Multiple roads were closed because the Back River was out of its banks.
Flooding on McIntosh Run near Potato Farm Rd. Water is 2-3 feet deep and approximately 600 feet wide.
The river gage on the Western Branch Patuxent River near Upper Marlboro, MD exceeded the 11 foot flood stage during the indicated period. Much of Race Track Rd. flooded between Marlboro Pike and the community center. The peak level of 13.04 feet occurred at 8:15 PM on the 4th.
The river gage on Mattawoman Creek near Pomonkey, MD exceeded the 7 foot flood stage during the indicated period. Pomfret Rd. is flooded and closed. The peak level of 8.06 feet occurred at 11:00 PM on the 4th.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Tropical Storm, St. Mary'S | 2020-08-04 | Vehicle/Towed Trailer | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2020Every state in 2020This day in weather historyThe tornado archive for Maryland, 2020Warnings in Maryland, August 2020The 2020 hurricane season
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 918685, 918700, 918716, 918721, 918722, 919467, 919471, 919477, 919485, 901058, 901059, 918924, 905440, 915301, 901057, 915302, 915518, 916813, 915520, 915521, 915522, 915523, 915524, 915527, 915538, 918376, 916803, 915530, 915541, 916801, 915550, 915532, 915552, 918377, 915555, 915559, 915561, 918379, 918382, 918385, and more.