Above: Infrared satellite image of Invest 93L (now Tropical Depression 3) at 1736Z (1:36 pm EDT) Monday, June 1, 2020. (NASA/MSFC Earth Science Branch)
At least 17 people have died from flooding in El Salvador and Guatemala linked to short-lived Tropical Storm Amanda, which slogged ashore shortly after it formed on Sunday. At midday Monday, Amanda's remnants were moving from the Yucatan Peninsula toward the Bay of Campeche, where a new tropical cyclone may form as soon as Monday night. Advisories on Tropical Depression 3 were launched at 5 pm Monday by the NOAA/NWS National Hurricane Center. Update (12:30 pm EDT Tuesday): Based on hurricane hunter observations, TD 3 has just been upgraded to Tropical Storm Cristobal. We'll have a full update later today. As of 12:15 pm EDT Tuesday, Cristobal was centered about 150 miles west-southwest of Campeche, Mexico, drifting southwest at 3 mph, with top sustained winds of 40 mph.
Ernesto Muyshondt, the mayor of El Salvador’s capital city, San Salvador, said 50 houses had been destroyed in the city, and officials said hundreds of people around the country had been evacuated as rivers overflowed. See the weather.com article for updates on the flood impacts in and around El Salvador.
More flooding—potentially major—is possible across Central America in the coming days, depending on the evolution of a complex circulation over the region.
In a tropical weather outlook issued at 2 pm EDT Monday, June 1—the official start day of the Atlantic hurricane season—the NOAA/NWS National Hurricane Center put 90% odds on formation of at least a tropical depression by Wednesday from Amanda’s remnants, which were dubbed Invest 93L. The center added: “…a tropical depression or storm is likely to form tonight or Tuesday.”
Satellite imagery at midday Monday showed plenty of mid-level spin over the Yucatan Peninsula, with convection waning after a typical overnight peak. The peninsula is one of those rare land features that can sometimes support weak tropical disturbances, as noted by Eric Webb (@webberweather). There were signs of a low-level circulation center trying to take shape near the peninsula’s west coast as the loosely organized system drifts west-northwest.
Outlook for TD 3: Plenty of slow-burn uncertainty
Sea surface temperatures (SSTs) over the Bay of Campeche are amply warm—running 28-29°C (82–84°F), which is about 2-3°F above average for this time of year—and the atmosphere is very moist, with mid-level relative humidity around 80%. The concave topography of the Bay of Campeche helps concentrate cyclonic circulations, which often gives systems like this a boost.
One potential impediment to rapid development is strong wind shear, expected to run at around 15-20 knots through Monday night. However, the axis of strong shear will be lifting northward over time, and wind shear may drop into the 10-15 knot range on Tuesday. By that point, upper-level winds related to the shear might provide an outflow channel that would favor development.
Models suggest that TD3 will continue to move slowly westward while gradually angling to the left, pivoting around the north side of a massive circulation feature called the Central American Gyre. CAGs tend to develop near the start and end of the Atlantic hurricane season, as large-scale weather features rearrange themselves during the waxing and waning of northern summer. CAGs tend to have relatively weak surface winds, but they can sprawl over hundreds of miles, and they are notoriously long-lasting and slow-moving, both of which make them dangerous rain producers.
Amanda and its remnants have been on a multi-day trek around the gyre, moving from its south to east to northeast side as the CAG itself drifts northward. If the CAG remains the dominant steering feature, we could expect TD 3 to move southwestward into Mexico later this week. However, it’s also possible that TD 3 will stall out and feel the tug of steering currents to the north, which could eventually pull it away from the CAG and bring it into the Gulf. This solution is reflected in the official NHC forecast at 5 pm EDT Monday (see below).
Still another possibility is that TD 3 diminishes or moves inland, and another “spoke” of the gyre develops and moves north into the Gulf.
Our top long-term models for tropical genesis, the GFS and European, each have a majority of ensemble members bringing some feature slowly northward across the western Gulf over the next week or so. This may be the most plausible conclusion in a forecast packed with uncertainty.
Although SSTs are above average throughout the Gulf of Mexico, oceanic heat content is still relatively modest outside of the southeast Gulf, given that we are still in astronomical spring (see above). This lack of high heat content would reduce—though not eliminate—the chance of rapid intensification of a northward-moving Gulf system. Values above 75 kJ/sq cm are most closely associated with higher odds of rapid intensification, but we often see rapid intensification when OHC is between 50 and 75 kJ/sq cm.
There is already some model signal for a swath of moisture displaced on the far east side of any eventual northward-moving system, so if anything does develop in the Gulf, its heavy rains may have an unusually broad reach.
If TD 3 becomes a tropical storm, it would be named Cristobal—and should that happen before Friday, it will be the earliest third (“C”) storm in Atlantic records going back to 1851, beating out Tropical Storm Colin (June 5, 2016).
