BMS Tropical Update 9/18/2017 12 PM CDT

By: - September 18th, 2017

Although there are no current threats to the U.S. mainland, I would like to provide a brief update on the thoughts that were discussed in Friday’s Tropical Update.

Below are a few key points about each tropical system:

Tropical Depression (TD) Lee:
TD Lee is currently 1060 miles west of the Cabo Verde Islands and is a weak tropical depression. It has weakened significantly since being named a tropical storm on Saturday morning and is now battling dry air and wind shear. Lee is expected to dissipate over the next 24 hours and will not likely be a threat to the insurance industry.

Hurricane Jose
Jose is currently 265 miles east-southeast of Cape Hatteras, NC and is moving north at 9 mph. It is currently a Category 1 hurricane.

Jose continues to show signs of weakening on satellite imagery as dry air is wrapped into the circulation. It will likely continue to weaken as it moves over increasingly cold water, as discussed on Friday. It should turn into a subtropical system later this week.

The outer bands of Jose will arrive on the coast between Boston and Cape Hatteras on Tuesday morning. These bands will feature breezy conditions and light/moderate rain. Overall, there should be minimal impact on Tuesday as rain bands continue to rotate onshore.

The one area of concern that’s been a given since the beginning loop early last week are the large waves that will continue to pound all ocean facing beaches in Delaware, New Jersey, Long Island, Rhode Island, and Massachusetts. Beach erosion will be an issue for the typically at-risk areas. Additionally, astronomically high tides will fuel coastal flooding concerns for low-lying areas as persistent onshore winds push a slight storm surge into eastern Massachusetts and the Long Island Sound. Waves and surge will gradually subside on Thursday as the storm weakens.

Beyond Thursday, Jose will become trapped between two upper level systems. As a result, it will linger off the New England coast as it weakens due to the cold waters in the region. In the long range, there is a chance that its remnant moisture could loop around back into coastal New England and play a role in Maria’s long-term forecast, as discussed in more detail below.
At this time, the threat of major insured loss from Jose is low.

Hurricane Maria

Hurricane Maria, which was Invest 96L when discussed on Friday, was my biggest concern due to its track toward the Windward Islands. It is now 60 miles east of Martinique as a Major Category 3 with sustained winds of 120 mph.  Rapid intensification is still expected today and it looks like Maria could have a small eye suggesting a tight central core with very strong winds.

These continued signs of intensification are likely due to  warm waters not affected by Irma up-welling.  Richard Dixon @catinsight has put together a nice little graphic showing that there is currently little overlap across the Caribbean islands between the hurricane-force winds from Hurricane Irma and the forecasted wind swath for Maria. The overlap could occur near Puerto Rico, which will likely be impacted by Maria as a major hurricane on Wednesday of this week.


In the long range forecast, Maria still has some uncertainty not only in intensity but also with its future track. These go hand and hand. There is a chance that Maria could be weakened by the high topography of Puerto Rico, depending on its track over the island. Parts of the various ensemble model guidance from last night showed Maria moving west and dissipating over the high mountains of Hispaniola and Southern Cuba. Some model guidance also points to a Florida landfall or potentially even a track into the Gulf of Mexico. Many more ensemble members point Maria up the eastern seaboard, with impacts spreading all the way to the mid-Atlantic. Finally, the storm could recurve out to sea before impacting land. So, which of these scenarios is most likely in the long range?

All the ensemble runs from last night showing all the possible tracks for Maria. Currently there is only a 5-10% of landfall given the ensembles Map provided by Allan Huffman and models.americanwx.com

To understand that question we need to look at the bigger atmospheric pattern. The upper level forecast map from the ECMWF for Thursday shows a complex and highly amplified pattern over North America.

ECMWF forecast for this Saturday with highlights of the different features that will determine Maria’s future track.

The jet stream will be in what’s called a meridional flow pattern with high amplitude waves. This pattern is being driven by the recurvature of Typhoon Talim, which was previously discussed, and tends to cause a trough of low pressure to form along the East Coast 6-10 days later. However, it would appear that the blocking high pressure over the Great Lakes will attempt to stay in place. Jose will stand in the way from the high building back to the East. Therefore, this will likely create a weakness in the ridge. How quickly Jose can either leave the scene or weaken will have a huge impact on how quickly the ridge can rebuild, and thus will play a role in Maria’s track over the long range.

It appears at this point that Jose will be around until this weekend, which should attract Maria up to the east of the Bahamas. Maria will likely follow the path of least resistance around the Bermuda high and the weakness Jose has produced within the high pressure along the western part of the Atlantic Ocean. This would keep Maria away from the U.S. coastline. Although it currently looks like Maria will stay away from East Coast of the U.S., there is still some uncertainty in the long range. The overall forecast pattern is complex with several moving puzzle pieces that will come together later this week.

The insured impact from Maria will be high in the short-term as it will be a major hurricane when it interacts with some of the Caribbean islands yet to see impacts this year. Puerto Rico will likely take a direct hit from Maria.  The last such major hurricane was Hurricane Hugo 1989.


The insured impact in the long-term is unknown at this time, given the uncertainty in the forecast.  Currently there is only a 5 – 10% chance Maria would make U.S. landfall given the current ensemble forecasts.

Other Tropical Troubles

There is nothing else to worry about at this time off the coast of Africa.  Lots of dust and dry air and little convection over Africa.

Current Dust Layer from http://tropic.ssec.wisc.edu/

The next tropical development could occur near the coast of central America later next week, but this is with low confidence and little model support in the long range. However, this is an area to watch as October approaches, when the Main Development Region (MDR) tends to shut down and new named storm development tends to form in the western Caribbean as climatology suggests below.

Source: http://www.nhc.noaa.gov/climo/

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