Historic rainfalls associated with tropical moisture and a surface low pressure system inundated portions of South and North Carolina over the weekend. During the first four days of October, Charleston SC had 17+” of rain, Downtown Charleston had more than 16″, Columbia had 11″, Myrtle Beach had 14″. In fact, new records were set for greatest 1-day, 2-day, 3-day and 4-day rainfall at Charleston and Columbia (and storm-total rainfall amounts were as high as 26.88 inches in Charleston county;  click here for a YouTube video showing radar reflectivity from 1-6 October). The toggle above shows the Suomi NPP VIIRS Day/Night Band (with and without 24-hour precipitation totals ending 5 October, after the heaviest rain had moved north of Charleston) and Suomi NPP VIIRS 11.45 µm infrared imagery at 0630 UTC (2:30 am local time) — overshooting tops are evident within a band of strong convection offshore that was moving westward (inland) around the upper-level low pressure system located east of Jacksonville FL (as seen in the larger-scale version of the Day/Night Band image below).

The animation of GOES-13 10.7 µm Infrared imagery, below (click to view mp4 loop; very large animated gif file available here; a YouTube video of all GOES-13 RSO Infrared magery from 1-4 October is here), shows the evolution of the atmospheric flow pattern, from thunderstorms moving southwest-to-northeast along the coast on 1 October to thunderstorms moving directly inland, first from southeast-to-northwest late on 3 October and then to east/northeast-to-west/southwest along the coast at the end of the animation as an upper-level low developed east of Jacksonville. Multiple rounds of heavy rains occurred as the orientation of the rain bands pivoted, always overlapping South Carolina.

Much of the rain over Charleston fell between 0300 UTC on 3 October and 0700 UTC on 4 October, in two distinct events, as shown in the hourly GOES-13 Infrared image animation below. During the first bout of heavy rain that occurred late on the 2nd/early on the 3rd of October, cells moved over Charleston from the south; during the second bout of heavy rain, from the 3rd into the 4th, cells moved over Charleston from the southeast (this toggle of Total Precipitable Water from the GOES Sounder shows the convection offshore in regions of abundant moisture). The change in direction of cell motion was driven by the development of an upper-level low pressure system, as shown in the Water Vapor Imagery animation farther below. Both the thunderstorms over South Carolina and the thunderstorms supporting the evolution of Hurricane Joaquin benefited from the very moist tropical air mass that was over the Atlantic Ocean off southeast coast of the US.

A composite of the MIMIC Total Precipitable Water product and WSR-88D radar reflectivity visualized using SSEC RealEarth, below, showed how the offshore plume of high TPW became very narrow and focused on South Carolina during the 44-hour period from 18 UTC on 02 October to 14 UTC on 04 October.

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Hurricane Joaquin moved slowly through the eastern Bahamas on 1 and 2 October 2015. ASCAT data from 1356 UTC, above, shows rain-flagged values near 90 knots not far from the storm center (Joaquin is a potent Category 4 Hurricane; its strongest winds are confined to within about 50 miles of the center).

Joaquin is embedded within a very moisture-rich environment, and that tropical moisture will move inland over the Carolinas and surrounding states over the weekend and produce heavy rains. The animation of MIMIC Total Precipitable Water, above, shows a corridor of very high total precipitable water just offshore of the Carolinas at the end of the animation, ready to shift inland.

Water Vapor Imagery, below, shows a strong trough over the northern Gulf of Mexico. This trough is serving to move Joaquin out of the Bahamas, and it will also serve as a potent precipitation producer on the East Coast. Percent-of-Normal plots from NESDIS’s Blended Precipitable Water product shows a large region of nearly 200% of normal over South Carolina, and greater than 200% of normal over North Carolina and regions north and east. Flood Watches have been issued from northeast Georgia to southern New Jersey.

For the latest information on Joaquin, consult the National Hurricane Center. Additional information is available at the CIMSS Tropical Cyclones site, and in a previous Blog Post.

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The YouTube video embedded above shows all GOES-13 (GOES-East) Full Disk Water Vapor (6.5 µm) images for all of September 2015. The 10.7 µm Infrared window channel animation is shown below. Animations for GOES-15 (GOES-West) are at the bottom.

GOES-13 animations show more tropical activity over the Atlantic, as expected from climatology, during September compared to August.

The GOES-15 animations show many tropical cyclones in both the eastern and central Pacific Ocean. Indeed, 2015 ranks as the most active year for the central Pacific for Tropical Cyclones (Hurricane Oho, now south of Hawaii, is the 12th named storm of the year).

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Joaquin reached Category 1 hurricane intensity on the morning of 30 September 2015 (NHC advisories). An eye structure was becoming apparent on a 1259 UTC Microwave (85 GHz) image from the SSMIS instrument on the DMSP-18 satellite (above).

The GOES-13 (GOES-East) satellite was placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-7 minutes. Visible (0.63 µm) images (below; also available as an MP4 movie file) showed a number of convective bursts during the day, with a few overshooting tops.

GOES-13 Infrared (10.7 µm) images (below; also available as an MP4 movie file) showed that cloud-top IR brightness temperatures associated with these convective bursts were in the -80º to -90º C range (violet colors). An organized eye structure was beginning to appear on the IR images at the end of the day.

===== 01 October Update =====

The ASCAT Scatterometer on board METOP-A sampled the eastern half of Joaquin shortly after 0230 UTC on 1 October, as shown below. Hurricane-force winds were observed 20-30 miles away from the storm center; tropical storm-force winds extended about twice as far out.

Joaquin intensified into a Category 4 hurricane late in the day on 01 October (ADT intensity plot) as the storm slowly moved of the warm sea surface temperature and high ocean heat content waters in the vicinity of the Bahamas. Joaquin became the first Category 4 hurricane to move though the Bahamas in October since 1866 (Capitol Weather Gang blog).  A fairly persistent but rather ragged-appearing eye was seen on GOES-13 Infrared (10.7 µm) images (below; also available as an MP4 movie file). Once again, the well-defined eye structure was more evident on DMSP SSMIS microwave imagery.

GOES-13 Visible (0.63 µm) images (below; also available as an MP4 movie file) showed a continuation of the development of convective bursts with overshooting tops in the eyewall region of the hurricane.

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