The earliest “C” Atlantic tropical cyclone on record is unleashing catastrophic flooding across Central America and threatens to deluge the US Gulf Coast this weekend through early next week. Tropical Storm conditions appear increasingly likely beginning this weekend from Louisiana to the Florida panhandle.
Cristobal was ravishing southeast Mexico, Guatemala and El Salvador Thursday afternoon despite weakening into a tropical depression over the rugged terrain of the Yucatan Peninsula. Rainfall on the order of feet has fallen over portions of Guatemla, El Salvador, and Southeast Mexico since last Friday’s initial onslaught of Tropical Storm Amanda, whose remnants redeveloped into Tropical Storm Cristobal on Tuesday. El Salvador alone has reported 27 deaths from flooding, mudslides, and structural collapses since Friday, a figure that is undoubtedly on the rise with an additional 10-20″ of rain on the way for Central America. Storm totals are expected to approach 35″ through Saturday, when Cristobal’s week-long wrath ends in Central America and begins to take aim on the United States.
Cristobal had sustained winds of 35 mph and was centered roughly 120 mi south-southwest of Campeche, Mexico with minimum central pressure of 998 mb as of 11am ET Thursday. At face value this storm hardly appears menacing. What has made Cristobal so formidable is its near halt in motion over southeast Mexico and Guatemala. The tropical remnants from which Cristobal was formed crossed Central America last weekend and redeveloped into Cristobal Tuesday, only for the newly formed tropical storm to loop counter-clockwise back onto land. The continuous presence of this system has resulted in rich tropical moisture being forced up Central America’s extreme terrain. Mountains, some as high as 14,000 feet in Guatemala, squeeze almost all moisture from the atmosphere as strong winds blowing against them are forced upward in a process known as orographic lift. This orographic lift has been ongoing for nearly a week, resulting in extreme rainfall totals.
Fortunately Cristobal will not produce nearly as extreme rainfall in the US. The Gulf Coast is notoriously flat and Cristobal’s strength will be limited. A weak upper-level trough of low pressure will work together with a building ridge of high pressure over the Caribbean to draw Cristobal from the Yucatan peninsula Friday and pull it into the Gulf of Mexico. Conditions will not be favorable for rapid intensification over the Gulf. Wind shear will act to disrupt Cristobal’s circulation while a modest influx of dry air from the trough acts to limit the latent heat release necessary for tropical cyclone intensification. However, sea-surface temperatures ranging from 82-87°F are plenty warm enough to overcome these hindrances to allow for slow intensification en route for the central Gulf Coast.
US impacts from eventual Tropical Storm Cristobal will begin Saturday as his outer bands sweep across the Florida peninsula. The focus of the heavy rain will remain off-shore until Cristobal nears the coast enough for its inner bands to sweep across the Gulf Coast beginning Saturday night. Cristobal’s forward motion will again slow Saturday night as it approaches a wall of high pressure over the Central US. Although it will still be offshore, the storm will be close enough for its heavy rain bands to deluge portions of the Gulf Coast from Louisiana to north Florida depending on its track.
Model guidance has recently been consistent in drawing Cristobal toward a landfall somewhere in Louisiana between Sunday afternoon and evening. Dry air entrainment from the west will keep the tropical storm’s heavy rain to its north and east flanks such that Texas will largely be spared. The most likely location for landfall as of Thursday afternoon is in southeast Louisana near the Mississippi River Delta. A track like this would bring tropical storm conditions from New Orleans to Pensacola with the heaviest rain extending further east toward Florida’s Big Bend, where diverging winds from Cristobal and Caribbean high pressure will bolster upward motion and resulting rain intensity.
WeatherOptics has summarized expected flooding severity and impacts on commerce from Cristobal in our proprietary WeatherOptics Flood Index and WeatherOptics Business Disruption Index. Values of these indices are presented across the Central Gulf Coast between Saturday night and Monday morning in the series of map below from our impact portal.
As suggested by our the plots above, the expected track of Cristobal would bring the most significant flooding and disruption to life to the Florida panhandle. The WeatherOptics Flood Index reaches a maximum value of 7 early Monday across portions of the Florida Panhandle, with a particular focus of flooding along the Ochlockonee River west of Tallahassee. A value of “7” means that it is safe to remain indoors but area rivers may reach major flood stage, basements may flood, and enough area roadways will become so flooded that it may be impossible to perform daily errands.
Our Business Disruption Index, which describes how the weather impacts day-to-day commerce, also briefly reaches a value of “7” along Florida’s Big Bend before landfall early Sunday. This means that the combination of gusty winds, heavy rain, low visibility, and likely flooding will make typical commerce extremely difficult by prompting travel hazards and delays, electrical outages, and minor structural damage.
Cristobal will likely make landfall late Sunday after briefly turning clockwise around the blocking high pressure sytem into the lower Mississippi Valley. Rain will continue along the Gulf Coast as Cristobal gradually weakens and escapes northward, but details about his eventual track into the Central US early next week is still uncertain. Regardless of track, heavy rain from Cristobal’s remnants is likely to exacerbate ongoing flooding along the Mississippi and Missouri Rivers.