Joaquin Still Gripping Bahamas; #NotJoaquin Dousing Carolinas, Virginia

A potentially historic rainfall event for the Carolinas has begun, with many locations set to receive between 1 and 2 feet of rain by early next week. An intense band of thunderstorms has set up across eastern NC and northeast SC, and cells are “training” northward through this N-S band, already leading to high rainfall totals. A station at North Myrtle Beach, SC, reported 8.03” in the 24 hours up through 6:24 pm EDT Friday. More than half of that amount (4.30”) fell during the last two hours of that period.


Figure 1. Composite NWS/NEXRAD radar image from 2215Z (6:15 pm EDT) Friday, October 2, 2015. Image credit: WU’s Storm app for iPad.

The culprits behind this unique event are an upper-level low cutting off across the Florida Panhandle; a preexisting frontal boundary along the U.S. East Coast; and a flow of deep, rich tropical moisture, including some from Hurricane Joaquin (see below), streaming into the region. As the upper low slowly moves across the region, a weak surface low will form along the boundary somewhere near the South Carolina coast, causing the most intense swath of rainfall to pivot around its north side across the Carolinas.

When the frontal zone hits the mountainous western part of the state, upslope flow will add to the rainfall intensity and exacerbate the potential for landslides and mudslides. Models suggest that the strength of the inflow of moist air into this system is at record or near-record values for the time of year; wind speeds at the 850-millibar level (about a mile above the surface) are projected to be as high as 75 mph by Sunday. The projected rainfall amounts are in line with these extreme values (see our morning post for more details).

Does the Carolinas storm qualify as a “nor’easter”? Strictly speaking, it does: the AMS glossary defines “nor’easter” (“northeast storm”) simply as “a cyclonic storm of the east coast of North America, so called because the winds over the coastal area are from the northeast.” The term is most often used in connection with winter storms at more northerly U.S. locations. Another term for the event, quickly taking hold on Twitter, is #NotJoaquin.


Figure 2. The Congaree River at Carolina Eastman, about 10 miles south of downtown Columbia, SC, is projected to approach its record crest of 126.9 feet by late Monday. Image credit: NWS Advanced Hydrologic Prediction Service.

Major coastal/tidal flooding under way in Hampton Roads
The lower Chesapeake Bay region of Virginia is seeing one of its worst flood events in years, as persistent onshore flow is pushing water into the region through multiple tidal cycles. Heavy rainfall in the vicinity is only making matters worse. Coastal and tidal flooding will persist during the weekend from New Jersey to North Carolina, with conditions expected to be the worst in coastal Virginia, including the Hampton Roads area surrounding Norfolk. Extensive street flooding has already been observed in many low-lying parts of the region, and the situation may deteriorate further over the weekend, especially as surface low pressure wraps up in the Carolinas and the onshore flow intensifies on Sunday. See our morning post for more on the particulars behind this unfolding situation.


Figure 3. Quinn Hurt looks across Atlantic Avenue as he attempts to cross the flooded street in Wachapreague, VA, on Friday, October 2, 2015. Wachapreague is located on the Atlantic shore toward the south end of the Delmarva peninsula. Image credit: Jay Diem/The Daily Times, via AP.


Figure 4. MODIS image of Hurricane Joaquin over the Bahamas as seen from NASA's Aqua satellite on Friday, October 2, 2015, at approximately 12:30 pm EDT. At the time, Joaquin had top winds of 130 mph. Image credit: NASA.


Figure 5. Hurricane Joaquin in the early morning hours of October 2, 2015, as photographed from the International Space Station. The lights of Miami are visible at the top. Image credit: Commander Scott Kelly, ISS.

Joaquin continues to rake Bahamas
Hurricane Joaquin was still hammering parts of the Central Bahamas late Friday. Joaquin is one of the strongest hurricanes known to affect the Bahamas during October, with Category 4 conditions affecting several islands for the better part of 24 hours. Joaquin was a Category 3 hurricane, with top sustained winds of 125 mph, as of the 5:00 pm EDT advisory from the National Hurricane Center. Joaquin was moving north at 10 mph, but infrared satellite imagery shows that Joaquin’s showers and thunderstorms have expanded and intensified over the last several hours, so heavy rain and high winds are no doubt continuing to strafe much of the Central Bahama Islands. Joaquin’s center passed almost directly over the island of San Salvador late Friday afternoon, as a weather station there reported a pressure of 944.3 mb (27.88”). The eyewall of Joaquin affected Crooked Island/Acklins Island (population 600), and Long Island (population 3,000) for many hours, and no doubt damage is heavy to extreme on those islands. A cargo ship named El Faro, with 33 crew members aboard, has gone missing en route from Jacksonville, FL, to Puerto Rico. The last report from the ship, on Thursday, indicated that it had lost power and begun to list while located near Crooked Island, which would put it in or near the slow-moving eyewall of Joaquin. Two Air Force Hurricane Hunter aircraft were unsuccessful in attempts to locate the ship on Friday afternoon.

Wunderground member ExumaMET, located on the island of Exuma, posted this update on Friday afternoon:

“Joaquin had been giving us one good final lashing that coincided with the flood tide. Some spots on Exuma are seeing 5-6 foot surges and an entire portion of George town is under water. The back of my house is protected by an extensive mangrove system and I actually have 5 foot swells running. Also there have been at least 2 cruising yachts that have sunk in George town with more that have broken their moorings and are either drifting or already on the rocks. Makes me thankful this storm did not come west an extra 20 miles. I can't get through to anyone in Williams town to find out what the damage is like... They are the closest to where [Joaquin] passed. Going on my 3rd day without power.”


Figure 6. Satellite image of atmospheric water vapor, collected at 1915Z (3:15 pm EDT) Friday, October 2, 2015. A narrow channel of strong upper-level southerlies is positioned near the U.S. East Coast, ahead of a distinct upper-level low cutting off near the Florida Panhandle (the low’s swirl is visible in the tan color, denoting relatively dry air). An outflow channel can be seen running from Joaquin to the mid-Atlantic coast. Well to Joaquin’s east is an upper-level low, and even further out is Invest 90L, incorporating remnants of former Tropical Storm Ida. Image credit: NOAA/NESDIS.

Out to sea (knock on wood!)
With the 12Z Friday guidance, we can pretty much put to rest the idea that Joaquin will directly strike the Carolinas, an outcome that most models were projecting as recently as two days ago. All of the major dynamical and statistical track models used by the National Hurricane Center were moving Joaquin toward the north and northeast from its current location. In addition, nearly all of the GFS ensemble members (GEFS) show the offshore track. Even the possibility of a glancing blow to Cape Cod now appears to be a far-fetched solution, although Joaquin could move close enough to intensify the high surf and strong wind that will already cover a vast area to the hurricane’s north.

If you only had Figure 6, and no other pieces of evidence, you might be hard-pressed to imagine that Joaquin will be going out to sea. The NW-SE orientation of Joaquin’s outflow suggests that the hurricane is being tugged in the direction of the U.S. East Coast by the very strong south-southwest flow present there. However, the weak upper-level low evident to the northeast of Joaquin is the key. As it moves north in tandem with Invest 90L, located further east, this low will help create a pathway for Joaquin to zip north-northeast, parallel to the U.S. East Coast but far offshore. Joaquin may lose some of its classic symmetry on satellite as it gains speed, although it will remain a potent wind-producer for several days to come. The hurricane will also send powerful swells toward the U.S. East Coast throughout the weekend and into early next week.

We’ll be back with our next update on Saturday afternoon.

Bob Henson and Jeff Masters