The tropics are teeming with activity well ahead of schedule
Tropical Storm Hanna lurks in the Gulf of Mexico in this satellite shot on Thursday evening, July 23, 2020. (RAMMB/CIRA)
Tropical Storm Hanna formed in the Gulf of Mexico on Thursday evening, and is set to impact the western Gulf Coast, particularly Texas, with heavy rains and the potential for strong winds and storm surge flooding. It’s one of three areas in the Atlantic that meteorologists are closely monitoring as the tropics roar to life after weeks of quiescence.
Tropical storm warnings are up from Baffin Bay in Texas north through Port O’Connor, including cities like Corpus Christi, Rockport, and Victoria. Elsewhere, it’s a tropical storm watch, stretching from near Padre Island to Galveston Bay.
Meanwhile, nearly 2,000 miles to the east, Tropical Storm Gonzalo is drifting west toward the Windward Islands. As of Thursday afternoon, Gonzalo was sputtering — but is still predicted to become the first hurricane of the 2020 Atlantic hurricane season.
If that’s not enough storminess for coastal residents to worry about, a third tropical system could soon materialize off the west coast of Africa, meaning the sudden spate of storminess is unlikely to end anytime soon.
[NOAA predicts Atlantic hurricane season will be unusually active]
Hanna’s naming Thursday evening obliterates the previous record for the earliest “H” storm in an Atlantic hurricane season, held by Tropical Storm Harvey. That storm formed on Aug. 3, 2005. The record-busy start to the 2020 hurricane season has also featured the earliest “C,” “E” and “F” storms on record — Cristobal, Edouard and Fay.
Gonzalo became the earliest “G” storm on record early Wednesday, beating out Tropical Storm Gert, which struck Mexico after forming in the Bay of Campeche on July 24, 2005.
On average, a season’s eighth named storm doesn’t spring up until late September. The mean date is September 24th, making Hanna two months ahead of schedule.
Tropical Storm Hanna: a homegrown tropical threat
Tropical Storm Hanna as seen from the GOES East weather satellite on Thursday evening, July 23, 2020. (Tropical Tidbits)
Close to home, all eyes were on Tropical Storm Hanna, which formed Thursday evening after organizing slowly throughout the day.
On satellite imagery, a mass of shower and thunderstorm activity was readily apparent over the central Gulf, a discernible swirl already steering isolated showers and thunderstorms as they pinwheel into areas between Florida and Louisiana. Counterclockwise inflow near the surface was feeding the brewing system, while outflow exiting the storm aloft fanned out clockwise.
Early morning “scatterometer” data had shown the system was struggling to organize earlier in the day, but evening aircraft reconnaissance flights found the storm more mature with stronger winds. The system was declared a tropical storm at 11 p.m. Eastern Time.
A system must have sustained winds of 39 mph or greater coherently organized about a well-defined center in order to be considered a tropical storm.
Scatterometer data from early on July 23 reveals a closed circulation within the developing tropical system in the Gulf. (NOAA)
The forecast from the National Hurricane Center predicts that Hanna will make landfall along the Central Texas coastline later Saturday into early Sunday as a tropical storm.
Tropical Storm #Hanna Advisory 5: Air Force Hurricane Hunters Find That the Gulf Depression Has Strengthened Into Tropical Storm Hanna. Tropical Storm Warning Extended Southward. https://t.co/VqHn0u1vgc
— National Hurricane Center (@NHC_Atlantic) July 24, 2020
Their forecast calls for Hanna’s sustained winds to peak at 65 mph, but if it grows stronger, there would be the threat of at least low-end storm surge flooding along the Texas coast.
It’s important to note that, while a storm’s maximum sustained winds are often found tightly-coiled about its center, heavy rainfall and flooding can affect a far wider area.
For the time being, inland flooding from heavy rainfall appears to be the primary concern with Hanna’s arrival.
The heaviest rain looks to fall between Corpus Christi and Matagorda Bay and then southwestward toward the Rio Grande, although some heavy rains will be possible for places like Houston and Galveston, too.
A widespread 3 to 5 inches of rain is a safe bet, with scattered higher totals likely, especially near the coast.
The German ICON model’s simulation of how much rain could fall associated with the developing tropical system in the Gulf of Mexico through Monday, July 27. Focus on the broad trend, and not exact amounts or placement of rain totals. (WeatherBell)
However, there is a chance that Hanna could intensify more than some meteorologists are forecasting presently, as few inhibitive factors stand in its way. Conditions are conducive to a spurt of speedy strengthening, which may even help Hanna approach hurricane strength.
If that ends up being the case, wind and surge impacts would increase in tandem.
Texas has been hit hard by the novel coronavirus pandemic, with Houston, Galveston and Corpus Christi all seeing an increase in cases, hospitalizations and fatalities during the past month. This need for precautions against the spread of the novel coronavirus adds another layer of complexity to the task of preparing for this storm and potential flooding.
Gonzalo may become the first Atlantic hurricane of 2020
Gonzalo appeared slightly less organized and more ragged on Thursday morning, July 26, 2020, as seen in this GOES East satellite image. (Tropical Tidbits)
On Wednesday, Tropical Storm Gonzalo formed over the open Atlantic about 1,200 miles east of the Windward Islands. It’s slowly churning west, but the diminutive system was fighting off dry air originating over the Sahara Desert, which is attempting to choke the system from the north.
Dry air has eroded the western side of Gonzalo’s incipient eyewall structure, leaving it susceptible to further disruption and potential weakening.
It looks like #Gonzalo‘s convective diurnal max did not go smoothly.
An AMSR2 microwave pass (0450 UTC) suggests Gonzalo ingested dry air from the west, choking off convection on 89GHz w/ Arc clouds seen on 37GHz. This leaves Gonzalo’s fragile core unprotected & susceptible. pic.twitter.com/Qz8l0lns2j
— Philippe Papin (@pppapin) July 23, 2020
On Thursday morning, the system had a small doughnut of 65 mph winds at its center; tropical storm-force winds exceeding 39 mph only extended outward 35 miles. According to the National Hurricane Center, Gonzalo is expected to continue gradual strengthening — if it can outrun the pernicious affects of the encroaching Saharan Air Layer — and could become the Atlantic’s first hurricane of 2020.
Gonzalo’s minuscule size makes it especially sensitive to subtle changes to its surrounding environment. Predicting its intensity will be a challenge as it drifts westward toward the Windward Islands. A hurricane watch is up for Barbados, St. Vincent and the Grenadines. That’s where winds surpassing 60 or 70 mph are possible, along with 2 to 4 inches of rainfall. Localized totals could top half a foot.
Uncertainty abounds after Gonzalo enters the Caribbean. A wide range of possibilities is supported by computer models, ranging between full dissipation to further strengthening.
A long season ahead
In this Sept. 4, 2017, a vehicle is submerged in floodwater in the aftermath of Hurricane Harvey in Houston. (David J. Phillip/AP)
At the same time, a third tropical wave will exit the coast of Africa on Friday, and it is projected to develop as it moves west this weekend.
Atmospheric scientists have warned that this season could be particularly active. This is due to factors including a developing La Niña event in the tropical Pacific Ocean, which tends to favor a more active Atlantic season, and above-average sea surface temperatures in what’s known as the “main development region” of the Atlantic. The warmer-than-average waters can provide more fuel for stronger, wetter storms that inflict more damage.
[NOAA predicts Atlantic hurricane season will be unusually active]
Warm waters also help enable tropical cyclones to rapidly intensify. Climate scientists have found the incidence of rapidly intensifying storms could become more frequent as waters continue to warm due in large part to human-induced climate change.
Andrew Freedman contributed to this report.
