Above: Radar image of Tropical Depression Cristobal at 1700Z (1 pm EDT) Thursday, June 4, 2020. The center of Cristobal is the swirl at lower center, over far northwest Guatemala. (National Meteorological Service, Mexico)
Grinding its way inland from the Bay of Campeche, Tropical Storm Cristobal has fallen prey to the effects of interaction with land. At 11 am EDT Thursday, the NOAA/NWS National Hurricane Center downgraded Cristobal to tropical depression status, with top sustained winds of 35 mph. Cristobal was located about 160 miles south-southwest of Campeche, Mexico, near the northwestern tip of Guatemala, moving east-southeast at just 3 mph. There were no watches or warnings in effect.
Torrential and prolonged rains continue to be the main threat from Cristobal. The storm came on the heels of Tropical Storm Amanda, which produced deadly flooding as it moved into El Salvador and Guatemala on Sunday. Both Amanda and Cristobal developed within the Central American Gyre (CAG), the large circulation that’s predominated across the region for more than a week. The CAG has been reinforcing the moisture and the persistent onshore flow across parts of Central America.
Before Cristobal clears the region, rainfall totals could reach the following, according to NHC:
—Mexican states of Campeche, Quintana Roo, Tabasco, and Yucatan: Additional 6 to 12 inches, isolated storm totals of 25 inches
—Mexican states of Veracruz and Oaxaca: Additional 5 to 10 inches
—Southern Guatemala and parts of Chiapas: Additional 15 to 20 inches, isolated storm total amounts of 35 inches dating back to Saturday, May 30
—El Salvador: Additional 10 to 15 inches, isolated storm total amounts of 35 inches dating back to Saturday, May 30
—Belize and Honduras: Additional 3 to 6 inches, isolated 10 inches
Outlook for Cristobal
Cristobal will continue to drift mainly eastward today, grazing the northern border of Guatemala, before it begins to feel the tug of increasing southerly steering currents from a weak upper-level trough now in the central Gulf that will be shifting west. As it heads north on Friday, Cristobal will parallel the west coast of the Yucatan Peninsula. It’s now looking more possible that Cristobal would remain over the Yucatan until it leaves the north coast around Friday night. Given the flat terrain of the peninsula, recently soaked by Cristobal’s rains, it is possible that some restrengthening could occur even before Cristobal moves entirely offshore, but that will depend in part on how much degradation occurs tonight into early Friday.
Once Cristobal moves into the Gulf, it will encounter warm sea surface temperatures of around 27°C (81°F), albeit with only modest amounts of oceanic heat content below the surface. Increasing wind shear will be pushing dry air into Cristobal’s large but disheveled circulation. All these factors imply that Cristobal is unlikely to dissipate but also unlikely to strengthen dramatically during its two-day trek over the Gulf. A mid-range tropical storm at landfall appears to be the most likely outcome.
Our top longer-term track models, the GFS and European, are in close agreement on Cristobal’s eventual track northward through the Gulf from late Friday to Sunday, with a landfall most likely around late Sunday somewhere between Houston, Texas, and Mobile, Alabama. The scenario cropping up most often in the GFS and European ensemble members, as well as in the 0Z Thursday operational runs, is a slowing and a leftward angling once Cristobal reaches the northern Gulf coast. Such a move could take the system across Louisiana from southeast to northwest, followed by a likely acceleration into a midlatitude storm racing across the Great Lakes by midweek.
There’s been a strong suggestion in the GFS that Cristobal will have one or more embedded circulations spinning around a broader envelope as the complex moves across the Gulf. It also appears that Cristobal will be a lopsided storm, with heavy rains and wind/wave effects extending well ahead of its approach and well east of its center. The upshot is that parts of Florida are in for several more days of heavy showers and thunderstorms before Cristobal clears the region. A slug of moisture well ahead of Cristobal has already been plaguing South Florida.
Heavy rain will also accompany Cristobal’s center as it moves inland, with coastal rains likely heaviest from southeast Louisiana to the Florida Panhandle. This area is currently in moderate to severe drought, so widespread major flooding is unlikely. Further inland, a corridor of 3” – 5” amounts and heavier embedded pockets may set up somewhere across the lower Mississippi Valley. The GFS model suggests that precipitable water could reach or exceed 2.5” near Cristobal’s remnants, which would be in record range for June if this reached locations such as Shreveport, Louisiana, and Little Rock, Arkansas. In Arkansas, soils are saturated and some rivers are already at minor flood stage, so flooding may be more likely there.
We’ll have to watch models closely for any signal of stalling near the Louisiana coast, but at present it appears Cristobal will keep moving, thus limiting the flood threat.
CSU ramps up its 2020 Atlantic hurricane outlook
The forecasters at Colorado State University have boosted their projections for Atlantic hurricane activity in 2020 from their initial outlook issued in April. The latest outlook, released Thursday, is calling for 19 named storms (including the three already named), 9 hurricanes, and 4 major hurricanes, with accumulated cyclone energy (ACE) predicted to total 160. The total number of hurricanes has increased by one from the April outlook, and the predicted ACE is up from 150.
CSU’s June outlook has a more robust record of accuracy than its April outlook. This year’s outlook includes a new statistical scheme that performs quite well (correlation coefficient of 0.72) when used to “hindcast” activity for the years 1982-2019. However, it’s not bulletproof: as shown in the figure above, ACE was below average in 2006 despite an ACE forecast even more bullish than this year’s. Even so, most seasons with a high ACE prediction ended up with a high ACE total. The only year in which activity outperformed an ACE forecast of 160 or better was 2017.
Lending further support to CSU’s ramped-up outlook is the array of seasonal outlooks from public, private, and university forecasting groups, as compiled by the Barcelona Supercomputing Center. All 21 outlooks (see below) are calling for a more active season than usual.
Moreover, the tropical Atlantic appears to be moving toward La Niña conditions even faster than expected. Sea surface temperatures in the benchmark Niño3.4 region have fallen substantially below average over the past several weeks, and SSTs are now below average throughout the central and eastern tropical Pacific as of June 1, with the equatorial region dominated by cooler-than-average waters below the surface. La Niña events tend to support hurricane development in the Atlantic by fostering subsidence in the eastern Pacific and decreased upper-level wind shear over the Atlantic.
All things considered, it looks like we’re in for a busy few weeks.