Tropical Storm Cristobal is swirling northward, on course to make landfall in western Louisiana on Sunday night, after causing deadly flooding parts of Central America from more than two feet of rainfall.

The expansive storm, which has already set a record as the earliest third-named tropical storm or hurricane in any Atlantic hurricane season to date, has been slowly intensifying as it churns toward the coast. As of 11 a.m. Eastern time, the center of Cristobal was located 345 miles south of the mouth of the Mississippi River and was moving north at 12 miles per hour. Additional slow intensification is forecast.

Cristobal’s greatest threats will be water-related, both in the form of coastal flooding from the storm surge accompanying its landfall as well as inland flooding from heavy rains. Strong winds could cause damage along coastal areas in particular, with tropical storm warnings in effect for cities including New Orleans, Mobile, Ala., and Pensacola, Fla. However, with forecast maximum sustained winds at landfall of 60 miles per hour, winds are unlikely to cause severe, widespread damage.

Despite unusually warm sea surface temperatures, Cristobal is not in an ideal environment for rapid intensification, with strong upper level winds taking its toll on the structure of the storm, along with dry air that’s getting pulled into the circulation.

A clue about the storm impacts comes from Cristobal’s appearance on satellite imagery. Cristobal does not have a conventional appearance of a tropical cyclone, since instead of a symmetrical circle of thunderstorms surrounding its center, it more closely resembles a comma, with the heaviest rains and strongest winds displaced to the northeast of the circulation center.

Storm surge could inundate parts of highly vulnerable Louisiana, Alabama, Mississippi and Florida.

The storm’s tropical storm-force winds, which extend outward more than 200 miles from the storm center, have stirred up a large expanse of the Gulf of Mexico, and will pile up water onshore as the storm makes landfall. Therefore, a storm surge warning is in effect for areas from the mouth of the Mississippi River to Ocean Springs, Miss. The zone is outside of New Orleans’s Hurricane and Storm Damage Risk Reduction System, which was put in place to help protect New Orleans from surge-related flooding after Hurricane Katrina devastated the city in 2005.

According to the National Hurricane Center, a storm surge warning means there is a threat of life-threatening inundation, from rising water moving inland from the coastline, during the next 36 hours.

Storm surge flooding will be an especially significant issue for areas along and east of the storm’s center.

A storm surge warning is in effect for areas from the mouth of the Mississippi River to Ocean Springs, Miss., including Lake Borgne. This includes the Mississippi coastal cities of Gulfport and Biloxi. Low-lying areas of southeastern Louisiana, which have been sinking into the Gulf because of sea-level rise and other causes, will once again be buffeted by high winds and water, making life in some small communities less tenable.

A storm surge watch is in effect for Indian Pass to Aripeka, Fla., as well as areas east of Morgan City, La., to the mouth of the Mississippi River.

The Hurricane Center is forecasting the following storm surge values, indicating water above ground level, if the peak surge hits at the time of high tide.

  • Mouth of the Mississippi River to Ocean Springs, including Lake Borgne: three to five feet
  • Ocean Springs, Miss., to Indian Pass, including Mobile Bay and Pensacola Bay: one to three feet
  • Indian Pass to Aripeka: two to four feet
  • Aripeka to Marco Island, including Tampa Bay: one to three feet
  • Morgan City to the mouth of the Mississippi River: two to four feet

Strong winds will rake a large swath of the Gulf Coast shoreline

A tropical storm warning is in effect for areas east of Morgan City to the border between Alabama and Florida, including Lake Pontchartrain and Lake Maurepas, while a tropical storm watch is in effect for Intracoastal City to Morgan City. Tropical storm-force winds are forecast to reach southeastern Louisiana as early as 8 p.m. Eastern on Saturday night, spreading further northward overnight. Strong winds will buffet downtown New Orleans, as well as Baton Rouge and coastal Mississippi and Alabama.

The Florida Panhandle will also see gusty southeasterly winds for an extended period of time, though most places may not see sustained winds at tropical storm strength of 39 miles per hour or higher.

Heavy rains are a major, life-threatening risk

Areas along the Gulf Coast as well as the southern Mississippi and Tennessee Valleys are preparing for drenching rainfall and potential flooding. Flood watches stretch from the Mississippi River Delta, including Baton Rouge and New Orleans, east to the Big Bend of Florida in the vicinity of Panama City and Tallahassee.

The Florida Panhandle and coastal Alabama could see two to four inches of rainfall with localized five-inch amounts, while rainfall totals in southern Mississippi and southeastern Louisiana, including New Orleans should broadly range between six and 10 inches. A few locations may eclipse a foot, courtesy of Cristobal’s torrential tropical downpours with rainfall rates approaching three to four inches per hour in the most intense tropical rain bands.

Although wind often dominates the headlines, the leading cause of fatalities associated with tropical cyclones such as Cristobal is not wind; instead, it is storm surge and freshwater flooding. The National Weather Service is warning people in flood-prone areas to have a plan and be ready to evacuate to higher ground if a flash flood warning is issued.

If higher rainfall totals are realized in the city of New Orleans with high rainfall rates, urban flooding could become an issue given the limited capacity of a pumping system to move water out of the city and into Lake Pontchartrain.

Rain bands were sweeping into coastal Louisiana on Saturday morning and even affecting the Gulf Coast of Florida, with thunderstorms pinwheeling in ahead of Cristobal’s broad counterclockwise circulation. Otherwise, rain will begin along the Interstate 10 corridor in southern Louisiana, Mississippi and Alabama during the afternoon and evening hours on Saturday.

The Weather Service is warning of a risk of significant flooding, particularly among small tributaries of the Mississippi River and other larger water bodies. According to a statement issued by the agency’s New Orleans Office: “Major rainfall flooding may prompt many evacuations and rescues. — Rivers and tributaries may rapidly overflow their banks in multiple places. Small streams, creeks, canals, and ditches may become dangerous rivers. Flood control systems and barriers may become stressed.”

The core of Cristobal’s heaviest downpours and more central rain squalls will begin to move ashore in southern Louisiana around sunrise on Sunday.

There is a growing risk that torrential rainfall could even make it significantly farther north, affecting places well removed from areas typically vulnerable to tropical cyclones. Cristobal’s remnants will track inland and fuel heavy downpours along a cold front arriving from the Plains, dropping a hefty swath of two to three inch rain totals as far north as the Canadian Border. Much of Arkansas, eastern Iowa, Wisconsin, and even the Upper Peninsula of Michigan by Monday and Tuesday.

A staple of Cristobal’s onslaught on Central America, where the storm pinwheeled for days, has been widespread copious rainfall, measured not in inches but feet across many areas. Ocotepec, a city in Mexico, picked up a measured 26.9 inches between May 31 and June 4 — the bulk of which fell between June 2 and June 4. On Thursday, June 5, the community likely saw another two to three inches.

Xpujil, a town in Mexico, recorded 23.5 inches during the same period of time, while Hopelchén saw 23.1 inches.

It’s likely that some more remote areas received as much as 30 to 35 inches of rainfall. Potent flooding and mudslides struck El Salvador, where at least 27 died, while excessive rains also resulted in multiple fatalities in Guatemala.

Tornado chances

There is also a chance that the change of wind speed and direction with height that Cristobal will generate east of its center could cause a couple of thunderstorms within the system’s spiral rain bands to rotate. That will present the threat of a few quick-hitting tornadoes or landfall waterspouts in southeastern Louisiana, coastal Mississippi, and extreme southwestern Alabama on Sunday. Rotation was visible on radar Saturday morning in the rain bands west of Tampa, Florida.

The Storm Prediction Center has outlooked places like New Orleans and Gulfport as being under a level 2 out of 5 slight risk for severe weather, including tornadoes, on Sunday.

Thereafter, a low-end tornado threat may accompany a few of the system’s remnant thunderstorms as they trudge up Mississippi and eastern Arkansas on Monday.