More than Two Feet of Rain in South Carolina; Joaquin Heads to Sea

The end is finally in sight for the epic multi-day rains that have pummeled the Carolinas over the last five days. Areas through the triangle from Columbia to Charleston to Myrtle Beach were especially hard-hit this weekend (see Figure 2). At least 9 flood-related deaths were reported across the Carolinas by Monday morning, and countless homes and cars were flooded. Transportation tangles continue across the region. As of 10 am EDT Monday, the flood had closed 391 roads and 165 bridges across South Carolina, according to the state’s department of transportation. This includes more than 70 miles of Interstate 26. Persistent high tides and coastal flooding have led to additional road closures in Virginia and Delaware. Highway 12, the main road connecting the Outer Banks, is closed in both directions at two points, near Ocracoke and Kitty Hawk, with reopening expected by 5 pm EDT Tuesday.

The upper low responsible for the epic rains is finally pushing offshore into the Atlantic, but extensive wrap-around rainbands continue across southeast North Carolina, with more widely scattered showers and storms across South Carolina. Short-range models hint that today could bring a final dose of rain totaling more than 1” in spots along a swath from near Columbia, SC, to Hatteras, NC.


Figure 1. A vehicle and a home are swamped with floodwater from nearby Black Creek in Florence, S.C., Monday, Oct. 5, 2015 as flooding continues throughout the state following several days of rain. Image credit: AP Photo/Gerry Broome.


Figure 2. 7-day rainfall totals for the period from 12Z (8:00 am EDT) Monday, September 28, through Monday, October 5, 2015. Observations are analyzed on a 4 km by 4 km grid using data from raingauges and NWS/NEXRAD radar, with supplementation by satellite data as needed. Image credit: NWS/NOAA Advanced Hydrologic Prediction Service.

How the numbers are stacking up
The heaviest 24-hour rainfall at downtown Charleston happened to fall from midnight Friday night to midnight Saturday night: 9.25”. This total fell short of the record for any 24-hour period, which remains 10.57” on Sept. 6-7, 1933. (The calendar-day record also stands: 10.38” on June 11, 1973.) WIth nearly nearly four weeks left in October, Charleston may yet approach its jaw-dropping monthly record of 27.24”, set in June 1973. According to WU weather historian Chris Burt, Charleston has the longest period of record for precipitation observations in the United States. Although the record is discontinuous, rain/snow observations began almost 300 years ago in Charleston. They extend from 1738 to the present (including the entire Civil War) except for the periods 1766-1784, 1792-1806, and 1812-1831.

The rains weren’t quite as heavy at the official reporting station in Columbia, but they managed to give the city its wettest calendar day on record: 6.87” on Oct. 4, 2015 (old record 5.79” on Jul. 9, 1959). Columbia also notched its wettest two-day period on record: 10.44” on Oct. 4-5, 2015 (old record 7.69” on Aug. 16-17, 1949).

From the Columbia area east to Georgetown, several Weather Underground PWSs have racked up impressive totals, consistent with Figure 1 above.



Nick Wiltgen (The Weather Channel), who compiled a large amount of rainfall data from the region, notes that these totals appear to have clearly smashed the previous state record for 5-day precipitation, which had been 17.44” in downtown Greenville (Aug. 22-26, 1908). We’ll have to wait till Tuesday to see which station ends up on top, since any additional rain today will further boost the 5-day totals for October 1-5. A number of CoCoRaHS stations have racked up especially high storm totals, including the following (courtesy Dr. Greg Forbes, The Weather Channel):

26.88" - 6 NE Mount Pleasant, Charleston Co SC
25.50" - 3 SE Cainhoy, Charleston Co SC
24.75" - Kingstree, Williamsburg Co SC
24.10" - 3 SSW Shadowmoss, Charleston Co SC
23.74" - Longs, Horry Co SC
23.61" - 5 SSE Charleston SC
23.46" - 10 NW Kingstree, Williamsburg Co SC
22.02" - 1 NNW Limerick, Berkeley Co SC
21.45" - 3 SW Folly Beach, Charleston Co SC
20.75" - Millwood, Sumter Co SC
20.42" - 4 E Moncks Corner, Berkeley Co SC
20.28" - Gills Creek (Columbia), Richland Co SC

See also this link (not a permalink) to the latest public information statement from the National Weather Service office in Charleston, which includes many of the reports above. State and national climatologists would need to carry out further analysis to verify the accuracy of any weather station and confirm the validity of its reports before new champions are confirmed.

More than a thousand-year rain?
Using about a century of precipitation records, NOAA has constructed a Precipitation Frequency Data Server, which estimates how often we might expect to see extreme rainfall events recur. From this database, the three-day 1-in-1000 year rainfall amounts for Charleston and Columbia are 17.1" and 14.2", respectively. The 24-hour 1-in-1000 year rainfall amounts for Charleston and Columbia are 14.8", and 12.5", respectively. (Hydrologists would refer to a 1-in-1000-year rain as having a typical "recurrence interval" of 1000 years. The idea is that such events are not always separated by 1000 years; the same amount of rain could conceivably occur the very next year, or might not occur until thousands of years later.) Comparing these numbers to the data above, it appears that the one-day event may not have reached the 1000-year recurrence mark, but the 3- to 5-day cumulative totals of more than 20” easily exceeded it (see Figure 3 below). These totals actually suggest a recurrence interval well beyond 1000 years, but the NOAA database does not extend to longer time periods, in part because it becomes progressively more difficult to estimate the intervals as they become longer. Note that these recurrence interval calculations assume the climate isn't changing, which is incorrect. Global warming puts more moisture into the atmosphere, shifting the odds of extreme rainfall events like this to be considerably more likely.


Figure 3. Recurrence-interval curves for the area near Sumter, SC, as calculated by NOAA’s Precipitation Frequency Data Server. These estimates are based on NOAA’s Atlas 14 calculation of the expected recurrence frequency of rainfall events for various amounts and time periods. Across much of the northeast half of South Carolina, three-day amounts of 20” or more would easily top the 1000-year recurrence intervals. South Carolina’s data are based on the 2004 edition of Atlas 14, so they may not fully reflect the influence of recent climate change in boosting the likelihood of extremely heavy rain.


Averaged across the state as a whole, the wettest three calendar months in South Carolina weather history are July 1916 (14.41"), September 1924 (13.16"), and September 1928 (12.70"). All of these were related to tropical cyclones passing through or near the state. The last five days alone have already brought South Carolina close to the wettest month in state history--without a tropical cyclone landfall!

The Carolina rains are only the latest in a remarkable year of prolonged torrential rain events across parts of the United States. Texas and Oklahoma have already notched their wettest months on record (by far) this past May, and Illinois had its second-wettest month on record in June. Research has confirmed that our warming climate is making intense short-term rains (such as the highest 1-day totals) even heavier in many parts of the United States and the world, as warmer temperatures allow more moisture to evaporate from oceans and flow into rain-making storm systems. Less research has been done on trends in multi-day rainfall events, although the same general principle should apply. Just as warming temperatures are folded into the 30-year NOAA database used for calculating local average highs and lows, our increasing prevalence of extreme precipitation events can be expected to gradually shift the odds reflected in the recurrence intervals discussed above. It’s also possible that the ongoing El Niño event, which has intensified throughout 2015, has played a role in boosting the amount of water vapor available for heavy rains across the southern U.S. For more on the science of extremely heavy rainfall, see Bob Henson's May 2015 post, The Rains of May and the Science of Recurrence Intervals.

At Capitol Weather Gang, Jeff Halverson and colleagues have published an excellent first-cut analysis of the meteorology behind the Carolina rain event.


Figure 4. Satellite image Hurricane Joaquin (right) and the powerful low pressure system bringing heavy rain to the Southeast U.S. (left) taken at 9:15 am EDT October 5, 2015. At the time, the hurricane was a Category 1 storm with top winds of 85 mph. A band of very heavy rain can been seen feeding into South Carolina, to the west of the hurricane. Image credit: NOAA Visualization Laboratory.


Figure 5. Radar image of Hurricane Joaquin taken at 9:13 pm EDT October 4, 2015, from the Bermuda radar.

Hurricane Joaquin brushes Bermuda
Hurricane Joaquin passed 75 miles to the northwest of Bermuda on Sunday evening as a Category 2 storm with 100 mph winds, bringing tropical storm-force winds and heavy rain to the island. Bermuda International Airport reported sustained winds of 48 mph, gusting to 64 mph, at 1 am EDT Monday. Bermuda probably has the most hurricane-resistant infrastructure of anyplace on Earth, and I expect damage will be minimal on the island. Category 1 Joaquin is now speeding north-northeast out to sea, and will not affect any more land areas as a tropical cyclone. By Wednesday, Joaquin will evolve into a powerful extratropical storm, and will likely bring strong winds and heavy rain to Portugal this weekend.


Figure 6. Damage on Crooked Island in the Bahamas after Hurricane Joaquin as grabbed from a video posted to The Weather Channel.

Hurricane Joaquin heavily damages the Bahamas
Communications with the islands in the Bahamas most heavily damaged by Hurricane Joaquin are still tenuous, but it is clear that damage was heavy on Crooked Island, Acklins Island, Long Island and San Salvador. One death has been reported on Long Island due to high winds collapsing a home. The Coast Guard is still searching for survivors from the container ship El Faro, which is presumed to have gone down in the hurricane. One body from the crew of 33 has been recovered.

91L approaching Lesser Antilles with no signs of development
An area of low pressure (Invest 91L) centered at 8 am EDT Monday about 1000 miles east of the Lesser Antilles Islands is moving west-northwest at about 15 mph. Satellite loops show that 91L has a decent amount of spin, but almost no heavy thunderstorms. Wind shear is currently moderate, 10 - 15 knots, but will rise to the high range, 20 - 25 knots, on Tuesday and Wednesday, according to the 8 am EDT Monday run of the SHIPS model. One of our three reliable models for forecasting tropical cyclone genesis, the UKMET model, does develop 91L into a tropical depression late this week, as the storm heads northwards in the open Atlantic. 91L will bring heavy rain showers and gusty winds to the northern Lesser Antilles Islands beginning on Thursday morning. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 20%, respectively.

Tropical Storm Oho skirting Hawaii
In the Central Pacific, Tropical Storm Oho is churning the waters about 300 miles south of the Big Island of Hawaii. With wind shear expected to relax over the next few days, Oho has a chance to intensify from its current 50 mph winds to the threshold of Category 1 hurricane status, 70 mph winds, as it heads north-northeast to northeast. While the storm is not expected to threaten Hawaii, the Air Force Hurricane Hunters are scheduled to fly the storm Monday afternoon, and the NOAA jet will fly a dropsonde mission to aid in model forecasts for the storm. In their 11 am Wind Probability Forecast, the Central Pacific Hurricane Center was giving only one place in Hawaii odds of seeing tropical storm-force winds--South Point on the Big Island, with a 3% chance.

Tropical Storm Choi-wan headed towards Northern Japan
In the Western Pacific, Tropical Storm Choi-wan is expected to head northwards towards Northern Japan this week and potentially intensify into a Category 2 typhoon. Choi-wan will then likely weaken to a tropical storm before it reaches Northern Japan on Thursday.

Tornadoes from Typhoon Mujigae kill 6 in China
Category 4 Typhoon Mujigae made landfall on the north side of the city of Zhanjiang, China near 1 am EDT Sunday (05 UTC), with sustained winds of 130 mph. Several powerful tornadoes spawned by the typhoon killed at least six people (video and new story here.) Qingqing Li of the Pacific Typhoon Research Center, Nanjing University of Information Science and Technology, alerted me of these videos of the tornadoes as well:

http://video.weibo.com/show?fid=1034:bed4e4b67f0fd9a2396ca4564f38270a
http://video.weibo.com/show?fid=1034:eeb1fafeee6d502df3c947519469e728

Deadly flash flood hits the French Riviera
At least 19 people were killed as the much-visited southeast coast of France was struck by disastrous flash flooding along the French Riviera on Saturday night. Mediterranean resort towns beloved by jet-setting tourists, such as Cannes, Nice and Antibes, were devastated by the torrential weekend downpour, which trapped residents in cars, parking garages and retirement homes. Rivers of water gushed through some of the world's wealthiest streets, scattering cars hundreds of feet from where they were parked and destroying businesses in what were described as 'apocalyptic' scenes. After a river surged over its banks, three people were killed in a retirement home. In just one hour, Cannes received a record 107 mm (4.21”); the previous one-hour record was 70 mm (2.76”). Dew points surged into the lower 60s Fahrenheit on Saturday at Cannes. On Sunday, supercell thunderstorms tore across northern Italy as the front responsible for the French floods surged eastward.


Figure 7. Intense thunderstorms can be seen along the coast of the French Riviera in this infrared satellite image, collected at 1800 GMT (8:00 pm local time) on Saturday, October 3. Image credit: CIMMS/SSEC/University of Wisconsin.


Figure 8. A man walks past damaged cars, in Mandelieu-la-Napoule, southern France, on October 5, 2015 after floods tore through the French Riviera. Cars are often stacked in this manner in the aftermath of flash floods, as was the case during the catastrophic Rapid City, SD, flood of 1972 (scroll page for photo). (image credit: Rapid City Image credit: Anne-Christine Poujoulat/AFP/Getty Images.

Portlight disaster relief charity responding to South Carolina flooding
The South Carolina-based Portlight.org disaster relief charity, founded and staffed by members of the wunderground community, is responding to the devastating South Carolina floods by working with emergency management agencies to help ensure that those still stranded are brought to safety. They will be working with Red Cross shelters to ensure they're accessible to all, and as always, will be ready to replace lost or damaged medical equipment. If you're in South Carolina and you'd like to volunteer with them, please email the Operations Manager, Shari Myers, shari@portlight.org. You can follow Portlight's progress on the Portlight Blog. Please consider a donation to Portlight's disaster relief fund at the portlight.org website.

We'll have our next update on Tuesday.

Bob Henson (rainfall); Jeff Masters (tropical)

#flood #flooding #Cannes #tonight The streets all surrounding the #Palais were like #rivers 2ft+ deep in some places pic.twitter.com/hNOVcqJwQL

— John Henry Canavan (@JHCanavan) October 3, 2015