Above: GeoColor satellite image of Tropical Storm Cristobal at 2137Z (5:37 pm EDT) Friday, June 5, 2020. (tropicaltidbits.com)
Now moving north over the warm waters of the open Gulf of Mexico, Tropical Storm Cristobal is expected to gather strength as it heads toward an expected landfall in or near Louisiana late Sunday. Even before it moved off the Yucatan Peninsula, Cristobal was upgraded from a tropical depression to a tropical storm early Friday afternoon. Cristobal is a large, impressively organized tropical storm that will bring widespread impacts to the U.S. Gulf Coast.
As of 8 pm EDT Friday, Cristobal was located about 480 miles south of the mouth of the Mississippi River, moving north at 13 mph. Top sustained winds were 40 mph, making Cristobal a minimal tropical storm.
A tropical storm warning was in effect from east of Morgan City, Louisiana to the Okaloosa/Walton county in Florida (near Destin), including Lake Pontchartrain and Lake Maurepas, as well as for the stretch from Punta Herrero to Rio Lagartos on the east coast of Mexico’s Yucatan Peninsula, including Cancun and Cozumel. A tropical storm watch extended west from Morgan City to Intracoastal City. A storm surge warning was in effect from the mouth of the Mississippi River to Ocean Springs. Mississippi, including Lake Borgne, with storm surge watches for areas on either side – westward from the Mississippi to near Morgan City, Louisiana, and from Indian Pass to Arepika, Florida.
Now that Cristobal is pulling away from them, residents of southern Mexico and Central America will soon get a chance to dry out after a week-long siege of torrential rains. Another 3” – 6” is possible in some areas as Cristobal departs but southerly flow remains. Heavy rains have arisen from both Tropical Storm Amanda in the Northeast Pacific and Cristobal in the Atlantic, both of which were spawned from a huge Central American Gyre (CAG) feature. At least 34 flood-related deaths were reported from El Salvador, Guatemala, and Honduras in association with Amanda, Cristobal, and the CAG, according to the UN Office for the Coordination of Humanitarian Affairs (via ReliefWeb).
Over the last several days, the downpours have been especially heavy on Cristobal’s east side across and near the Yucatan Peninsula. Five-day rainfall totals for the period Sunday through Thursday include:
681.3 mm (26.82"), Ocotepec, Chiapis
596.0 mm (23.46"), Xpujil, Campeche
587.4 mm (23.13"), Hopelchén, Campeche
Track and intensity forecast for Cristobal
Cristobal’s acceleration into the Gulf simplifies a track forecast that had been complicated for several days by the storm’s slow movement over southeast Mexico. The storm now should continue moving northward at 10 – 15 mph until it reaches the coast of Louisiana on Sunday afternoon/evening. We can expect a slight leftward bend over time in that northward track, as Cristobal angles around a weak upper-level low in the western Gulf of Mexico. After landfall, Cristobal will gradually accelerate toward a strong midlatitude storm system pushing through the northern U.S. This should take the storm and its remnants north-northwest through Louisiana and Arkansas and then rapidly north-northeast into the western Great Lakes (it’s not often you see a 5-day NHC cone reaching Hudson Bay).
Cristobal will encounter a mixed bag of influences on its strength as it crosses the Gulf. It’s a well-structured storm with a large circulation, but the size of the wind field will actually impede rapid intensification, as larger systems take longer to spin up and spin down. There is also plenty of dry air lurking west of the storm, ready to be ingested, and this will likely disrupt showers and thunderstorms (convection) across Cristobal’s western half. Wind shear will be mainly light to moderate (5 – 15 knots), so if Cristobal manages to develop a compact inner core, that core might be able to wall off the effects of dry air to some extent. The storm will be moving over warm waters with sea surface temperatures of 27-28°C (81–82°F), although oceanic heat content below the surface is modest compared to what’s often present later in the summer.
All told, Cristobal is most likely to strengthen gradually rather than quickly, which points toward a probable landfall as a strong tropical storm, although Category 1 hurricane strength can’t be ruled out just yet.
Storm surge to be widespread across eastern Gulf
Cristobal’s broad and expanding wind field will push storm surge across the entire eastern Gulf Coast. The highest surge, perhaps 3 to 5 feet above tidal levels, is expected over southeast Louisiana and Mississippi east of the Mississippi River. As pointed out by Dr. Jeff Masters in a post earlier today, a surge of about 6 feet upriver would be required to top river levees in New Orleans, so overtopping is not a major concern unless Cristobal were to overperform in a big way (e.g., arriving as a Category 2 storm).
Surge flooding may occur as soon as Saturday’s midday high tide across the eastern Gulf. It will likely peak along the northeast Gulf Coast with Sunday’s midday high tide, with a secondary peak on Monday. Tides in some areas may remain elevated as late as Tuesday, as Cristobal continues to pull south winds against the coast even as it moves well inland.
Heavy rains from Cristobal to affect a broad area
It’s a good thing Cristobal is expected to stay on the move instead of stalling, because the storm is hauling an extremely moist air mass toward the Mississippi Delta. Predictions from the 12Z and 18Z Friday runs of the GFS model show that precipitable water (the amount of moisture in an imaginary column from ground level up through the atmosphere) could reach 2.7” – 2.8” over southeast Louisiana as Cristobal comes ashore. Such values would set a June record for the New Orleans area, where PW has risen above 2.7” only one time in May and a few times from August to October.
Rainbands from Cristobal are already streaming across the Florida Peninsula, and those should intensify on Saturday. More concentrated heavy rain will develop late Saturday on Sunday along the coast near and east of Cristobal’s track, from Louisiana across the Florida Panhandle, with widespread 3” – 5” totals. Localized amounts could top 10” across the Mississippi Delta in Louisiana and Mississippi, especially if Cristobal tracks as expected, so flash flooding could be widespread in and around the New Orleans area apart from any storm surge. Cristobal may leave a track of 2” – 5” rains along its inland path all the way to Ontario.
We’ll have our next full update on Cristobal around midday Saturday.
