May 27, 2020 – Short-lived Bertha Brought Heavy Rains to Parts of Florida
Bertha was a named storm for just the briefest of periods, becoming a tropical storm on the morning of Wednesday, May 27 at 8:30 am EDT just one hour before it made landfall along the South Carolina coast near Charleston. Using satellite and other observations, NASA calculated the large rainfall totals that it generated over parts of Florida early in its short lifetime.
After making landfall, Bertha quickly weakened into a tropical depression and was then accelerated northward by the southerly flow between a deep trough of low pressure over the Mississippi Valley to the west and a ridge of high pressure located just off the U.S. East Coast. Because of this, rainfall totals over the Carolina’s were not very heavy. Bertha’s biggest impact actually occurred when it was still in the formation process, before it became organized enough to be named.
On Monday May 25, a trough (elongated area) of low pressure became established over the Florida Straits, initiating shower and thunderstorm activity in the region. Over the next day, as this trough, which extended eastward over the warm waters of the Gulf Stream and eventually led to Bertha, slowly moved northward up the Florida peninsula, it provided a focus for showers and thunderstorms, which brought heavy rains to southeast Florida.
Calculated Rainfall Totals
NASA’s Integrated Multi-satellitE Retrievals for GPM (IMERG) algorithm, combines observations from a fleet of satellites, in near-realtime, to provide near-global estimates of precipitation every 30 minutes. IMERG surface rainfall accumulations were calculated for the period from May 23 to 27, 2020, for the southeastern U.S. The heaviest rainfall totals are located over southeastern Florida and the northern Bahamas where upwards of 150 to 200 mm (~6 to 8 inches) of rain are shown to have fallen. Miami received over 7 inches in one 24-hour period. Rainfall totals over South Carolina where Bertha made landfall, however, are much lighter on the order 25 to 50 mm (~1 to 2 inches) or more as the storm moved quickly on.
The rainfall calculation was visualized in an image produced with the Giovanni online data system, developed and maintained by the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC).
What is IMERG?
IMERG is a satellite-based rain estimate is somewhat coarse in resolution and can miss short-lived, intense storm-cells, but the IMERG algorithm often does captures the large-scale features of storms wherever they form in the world. While the United States is fortunate to have a network of ground radars that can provide higher-resolution precipitation estimates, in other parts of the world, notably over most of the world’s oceans, the IMERG rain estimate is an important reference point.
This near-real time rain estimate comes from the NASA’s IMERG algorithm, which combines observations from a fleet of satellites, in near-real time, to provide near-global estimates of precipitation every 30 minutes. By combining NASA precipitation estimates with other data sources, we can gain a greater understanding of major storms that affect our planet.
IMERG fills in the “blanks” between weather observation stations. IMERG satellite-based rain estimates can be compared to that from a National Weather Service ground radar. Such good detection of large rain features in real time would be impossible if the IMERG algorithm merely reported the precipitation observed by the periodic overflights of various agencies’ satellites. Instead, what the IMERG algorithm does is “morph” high-quality satellite observations along the direction of the steering winds to deliver information about rain at times and places where such satellite overflights did not occur. Information morphing is particularly important over the majority of the world’s surface that lacks ground-radar coverage.
Image from NASA Goddard using IMERG data archived at: https://giovanni.gsfc.nasa.gov/giovanni/.
May 27, 2o20 – NASA-NOAA Satellite Sees Tropical Storm Bertha Organizing
The second tropical storm of the North Atlantic Ocean hurricane season has formed off the coast of South Carolina. NASA-NOAA’s Suomi NPP satellite provided forecasters with a visible image of Tropical Storm Bertha as it was organizing.
On May 27, NOAA’s National Hurricane Center (NHC) issued a Tropical Storm Warning in effect from Edisto Beach, SC to South Santee River, SC.
The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard Suomi NPP provided a visible image of developing Tropical Storm Bertha late on May 26. The imagery showed strong thunderstorms were circling the center of circulation.
Satellite imagery on May 27 at 8:30 a.m. EDT showed the area of disturbed weather that NHC has been tracking over the past day or so quickly became better organized. The circulation had become better defined and the center had reformed beneath the area of deep convection. Those strongest storms were located just off the South Carolina coast.
At 8:30 a.m. EDT (1230 UTC), the center of Tropical Storm Bertha was located near latitude 32.7 degrees north and longitude 79.4 degrees west. Bertha’s center of circulation was just 30 miles (50 km) east-southeast of Charleston, South Carolina.
Bertha is moving toward the northwest near 9 mph (15 kph) and this motion is expected to continue through tonight. Maximum sustained winds are near 45 mph (75 kph) with higher gusts. Bertha is expected to weaken to a tropical depression after moving inland and become a remnant low tonight. The estimated minimum central pressure is 1009 millibars.
Bertha is expected to produce total rain accumulation of 2 to 4 inches with isolated totals of 8 inches across eastern and central South Carolina into west central to far southeastern North Carolina and southwest Virginia. This rainfall may produce life-threatening flash flooding.
NHC said, “The system will be moving inland very shortly and little, if any, additional strengthening is expected. Once inland, the small tropical cyclone should weaken rapidly and dissipate over central North Carolina on Thursday [May 28].”
Tropical cyclones/hurricanes are the most powerful weather events on Earth. NASA’s expertise in space and scientific exploration contributes to essential services provided to the American people by other federal agencies, such as hurricane weather forecasting.