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BMS Tropical Update July 11th

As mentioned in the last BMS Tropical Update, a storm is brewing in the Gulf of Mexico.  The National Hurricane Center has now named this system Tropical Storm Barry and expects it to potentially become a hurricane by Saturday and make landfall shortly thereafter, with possible impacts along the coasts of Texas and Louisiana, particularly in the city of New Orleans.  As many already know, New Orleans sits below sea level and has had its share of flooding problems in the past.  Since water is the new wind risk for the insurance industry, this BMS Insight will focus on this threat in a bit more detail, as any wind damage at this time is uncertain given the high forecast uncertainty around the overall intensity and track of the storm.

The forecast models are suggesting as much as 18 inches of rain for the region, which isn’t good, considering that the area is already inundated with rain. New Orleans has already flooded this week from rain, with many streets covered with a dangerous amount of water.  The Mississippi River is expected to rise to 19 or 20 feet by the weekend, which is near the height of the city’s levees.

By Saturday, it may have winds of 85 mph, making it a Category 1 hurricane on the Saffir-Simpson wind scale.  It should be noted, however, that there is a lot of uncertainty around the forecasted intensity of the storm. This intensity will depend on how much wind shear the storm encounters and how much time it spends over the warm waters of the Gulf of Mexico.  Currently, the worst-case scenario appears to be a Category 1 hurricane.  However, forecasts can change fast, as we experienced with Michael last year.  Most of the model guidance is suggesting a lopsided tropical storm with a landfall somewhere along the Louisiana coastline.

Wind speed is just one of the insured loss concerns from the storm.  Historically, flooding has not been a big concern for the insurance industry, but the take-up rates of flood insurance are higher in Louisiana, including New Orleans.  The reinsurance markets are taking on some of the risk from the National Flood Insurance Program, so this flood risk needs to be watched.  Also, coastal flooding tends to be the deadliest aspect of a hurricane.

The main concern here is that the storm surge combined with heavy rainfall could reach 3 to 5 feet, which would flood many of the low-lying areas of Louisiana.  This storm is expected to generate a lot of rain, with some areas potentially seeing more than a foot, which can contribute to inland flooding along the banks of rivers.

This is the current National Weather Service rainfall forecast over the next 7 days. This rainfall forecast will depend highly on the track of Barry
Current National Weather Service Forecast river level in New Orleans. This forecast will change with the track and intensity of Barry

The biggest threat from the storm may be in New Orleans, where the Mississippi River is already at 16 feet due to the very wet spring and summer upstream.  Some states along the river have seen their wettest spring in recorded history.  All of this water has worked its way down the Mississippi River, which has been high for well over a month now.  The National Weather Service is now predicting the river to crest at 19 feet on Saturday.  That is one foot below the top of the river levees. This could change given the track of the forecast. This morning the forecasted river height was 20 feet, so the forecast is changing for the better since the newest forecast is now one foot below the top of some of the levees.

So, why is this a concern?  During both Hurricane Katrina in 2005 and Hurricane Isaac in 2012, storm surge pushed well upriver. In those cases, however, the river was only at a level of 3 feet or less.  During Katrina, a Category 3 hurricane with top winds of 125 mph, the river swelled to at least 15.25 feet at the Carrollton Gage in New Orleans.  The gage stopped operating when the water reached that level.  Several barges were deposited on top of the levees in Plaquemines Parish during the storm by surge water.  During Isaac, a Category 1 hurricane with top winds of 80 mph, the river rose to 9.5 feet at the Carrollton Gage.  While the current river level in New Orleans is 16 feet, levees and floodwalls protect the city up to water heights of about 20 feet.

How high is a 20-foot-high river stage for New Orleans?  It is higher than 99.9% of the city’s land surface, higher than every human being except those in multi-story buildings and about 30 feet higher than the lowest neighborhoods.

The red dots show where levees in New Orleans are under 20 feet.  This is where over-topping of levees is most likely if the forecast of 19 feet comes to fruition on Saturday. The red dots on the north side of the Mississippi River flooded during Katrina, including the Lower 9th Ward.
These are the areas of New Orleans that flooded during Katrina.

In summary, the precursor for a bad flooding event is set for New Orleans and remains for much of the hurricane season.  Many areas of Louisiana are flat, and flooding is a big concern with this upcoming storm.  There is uncertainty at this time around the potential strength and track of the storm, which also increases the level of uncertainty around the storm surge that may be expected.  However, the rainfall forecasts have been fairly consistent over the last several days, with most of the heaviest rain expected to fall along with the storm’s forecasted path.

BMS Tropical Update: July 9th

There is an old proverb used to describe the Atlantic hurricane season: “June – too soon; July – stand by; August – come they must; September – remember; October – all over.” In fact, we suggested in our May BMS Tropical Insight that the next best opportunity for tropical storms was going to be in early July. It appears that June was indeed too soon for tropical threats to the U.S. coastline. However, with the start of July, that is expected to change with development appearing likely in the northern Gulf of Mexico later this week and into the weekend.

The NHC is giving an 80% chance of a Tropical depression forming in Gulf of Mexico later this week.


A precursor vorticity center (areas of spin) is currently heading south through Georgia and will emerge into the northeast Gulf of Mexico by Wednesday. This circulation will take advantage of warm water in the area to build thunderstorms and may slowly intensify into a tropical system.
Dry air and dust from a few major outbreaks of Saharan dust have battered most of the Atlantic basin for the last several weeks. This combined with strong wind shear has prevented tropical development across the Atlantic basin since Subtropical Storm Andrea briefly roamed the waters of the west-central Atlantic in late May.

With the Madden-Julian Oscillation (MJO) currently in a positive phase that supports upward motion over Central America, the absence of strong wind shear and warmer than normal waters across the Gulf of Mexico, it should not take much to organize a tropical named storm which, if it develops later this week, will be named Barry. For the last several days, the forecasted steering winds have suggested that any named storm would drift toward the central and western portions of the Gulf of Mexico this weekend. This would give it more time over open water and could potentially create a stronger storm. With this track the risk to the insurance industry grows due to the large amount of exposure in the Houston areas, the risk to offshore assets increases due to a number of petroleum rigs and refineries along the central and western Gulf Coast. Regardless of how much development we see, the forecast models are suggesting multiple days of showers and thunderstorms that could potentially bring flooding to the southern Plains, lower Mississippi Valley and/or the southern Appalachians starting this weekend and into next week, depending on the track and timing of the storm. Some models take the tropical storm as far west as Houston which has no issue flooding from even the smallest of weather systems. Currently, some of the guidance calls for 15″ of rain over the next 7 days for the area.

The overall model guidance from the ECMWF and GFS models have been back and forth over the last few days and the landfall location as suggested by the above GFS ensembles is anywhere from east Texas to Louisiana. Keep in mind this entire area will see a lot of rain.
Source: https://www.tropicaltidbits.com


The last time a named tropical system made landfall in the U.S. during the month of July was Tropical Storm Emily of 2017. Emily formed in the eastern Gulf of Mexico and moved into the central Florida Peninsula on the last day of July, so it’s not unusual to see the forecast of such an event happening this week. As I mentioned in our May BMS Insight, it appears that this season’s tropical activity will be more likely to develop closer to the U.S. coastline instead of out in the Main Development Region (MDR) of the Atlantic Ocean. The bigger question is just how much activity we’ll see this season as we move toward its climatological peak at the beginning of September.


Forecasters continue to call for five to eight hurricanes to develop this season. July still does not look like a very active period for named storm development, as large scale sinking air will continue over much of the Atlantic basin, along with on and off bursts of Saharan dust that may keep activity to a minimum. While El Niño conditions may suppress the total number of tropical storms and hurricanes in the Atlantic basin this season, the data is suggesting that El Niño is weakening and may become a non-factor as we head into September. With the warmest ocean temperatures right along the U.S. coastline, the insurance industry should continue to watch for tropical waves coming off Africa which could potentially strengthen into named storms when they get closer to the U.S. coastline versus the MDR in a more typical season.

Above are the different phases of the MJO and the influence on precipitation. Notice the red circled areas above. Tropical cyclones making landfall along the Gulf Coast during Phase 2 of the MJO during meteorological summer causes a statistically-significant positive precipitation anomaly to show up in the Deep South in the 1979-2008. Research here by Zhou et al.
Notice how the red circled areas match the forecasted areas for heavy rainfall over the next 5-7 days along the Gulf Coast.

We are also now in the period where the insurance industry can begin to watch the subseasonal forecast. I have mentioned before that one of the best ways to predict this is to use the MJO, which is a pulse of upward motion that travels the tropics but also creates areas of sinking stable air in other parts of the tropics. This symbiotic pattern of wetter and drier areas moves east as a unit and typically completes a full cycle in 45 to 60 days. When the MJO (or similar phenomena) promotes upward motion over the Atlantic, hurricane development and rapid strengthening becomes much more common. According to research performed by Phil Klotzbach of Colorado State University, hurricane damage in the U.S. during convectively active phases of the MJO since the early 1900s is nearly three times greater than during suppressed Atlantic phases.


Therefore, I believe the next round of tropical storms may begin during the second week of August. Based on the current state of African waves and favorable conditions for development along the U.S. coastline, we may also be seeing an active late September and early October. Until then, keep watching the skies off the Gulf Coast and along the southeastern U.S. for the development of named storms that might not coincide with the MJO phases.