BMS Tropical Update 9/20/2017 4 PM CDT

2017 Atlantic Hurricane Season Records Continue To Fall

The 2017 Atlantic hurricane season, which has already been memorable, continues to create long-lasting memories which will likely be talked about for decades. The newest talking point is Maria’s landfall at 6:35 this morning near Yabucoa, Puerto Rico. Maria arrived as a top end major Category 4 hurricane with maximum sustained winds of 155 mph and a pressure of 917 mb. Maria will likely be the strongest storm in terms of pressure to make landfall in Puerto Rico since 1928 – in terms of wind, it’s the second strongest. It is also the third most intense (by pressure) U.S. hurricane on record to make landfall behind Hurricane Camille, and the  Labor Day 1935 hurricane.

The statistics and images coming out of Puerto Rico indicate that Maria will likely be one of the largest natural catastrophes the island has ever experienced in terms of insured loss. But, I won’t dive into the devastation that has already occurred on the island, which is being covered extensively, but rather focus on the uncertainty of Maria’s long-term impact on the U.S. mainland.

Maria’s U.S. Mainland Threat

The geography of Puerto Rico has had a tremendous impact on Maria’s current intensity. The infrared satellite imagery above shows that the storm’s interaction with the high mountains has resulted in weakening, with a clear eye no longer visible. Unfortunately, this makes the storm no less dangerous, as winds well over 100 mph continue to beat the island. Torrential rainfall will remain as well, with totals nearing two feet in the higher terrain. Flash flooding and mudslides will be major issues for the next few days as Maria begins to move away from the island.

As Maria moves today toward the northwest, this weakening could influence the future track of the storm over the next week which, at this point, is still uncertain. A wobble south toward Hispaniola would result in a weaker system that may allow for a track farther west in the long term. The current forecast track takes the storm just north of Hispaniola, where the effect of land interaction would be minimal, thus keeping Maria on a more northwest track away from the East Coast of the U.S. next week.

The other complicating factor is the continued influence of Tropical Storm Jose, as discussed in my Monday update. Jose has already been a named storm for 15 days, which ties it for the 10th longest named storm since the beginning of the satellite era. Jose is still a large storm and, if it were not for Maria, would be a front-page news story. However, as I previously suggested, its insured impact has been minimal and similar to that of a nor’easter.

Currently Jose is doing another small loop off the New England coastline and is expected to continue to weaken over colder water as it moves back to the west later this week.

Reposting this image as the general ideas still holds from Monday thinking on overall pattern driving the northward turn of Maria.

Maria is expected to follow this weakness in the upper level ridge that Jose has created. However, the exact movement is a bit uncertain based on Maria’s trajectory away from Hispaniola and how far west Jose actually tracks. The general model guidance currently keeps Maria away from the East Coast. I do, however, expect the western edge of the National Hurricane Center’s cone of uncertainty to be very close to the coastline of North Carolina and Massachusetts as the five-day forecast cone expands northward over the next few days.

Right now, the forecast models have a bias that sometimes curve hurricanes northward  moving the hurricane to the northeast. If there is an error, it would result in a greater correction to the west with each model run.

Current long range track ensemble guidance from the American (GFS) and European (ECMWF) models. Most ensemble members keep Maria off the East Coast of the U.S. Some members however offer up landfall options all along the Northeast Coast of the U.S.

Currently, there is a 30% chance of U.S. landfall in New England per the American(GFS) ensemble model and a lower 10% chance from the ECMWF ensemble model. It should be noted, however, that cooler water temperatures and increasing wind shear will result in weakening of Maria as the storm moves northwest and then north this weekend. It would likely only be a Category 1 hurricane north of North Carolina.

Next Area Of Tropical Troubles

This is the next area to watch. This is the forecast valid for Oct 6th suggesting low pressure will be across the Western Caribbean

The next area to watch will be the western Caribbean, as the longer range models are suggesting tropical cyclogenesis in early October.

BMS Tropical Update 9/18/2017 12 PM CDT

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/

BMS Tropical Update 9/15/2017 12 PM CDT

More Tropical Troubles

First and foremost, I had previously mentioned several times I thought the Atlantic Basin would shut down for a few weeks due to the suppression phase of the Madden-Julian Oscillation (MJO). Unfortunately, the MJO is currently in a weakened state and the large-scale subsidence is not strong enough to overcome other climate forces that are allowing for new named storm formation in the Main Development Region (MDR). In this case, it could be tied to a convectively coupled Kelvin Wave which is likely enhancing the development of new named storms in the MDR.

Data suggesting a Convectively Coupled Kelvin Wave could be the climate forcer that is allowing for development in the MDR.

So, with the understanding that the insurance industry is still in the early stages of tallying the losses from Harvey and Irma, there might be a need to inquire about additional capacity for the remainder of the year. Therefore, I want to provide a bit more detail on what to expect in terms of tropical troubles for the remainder of the month.

Jose End Game

Hurricane Jose has been on the radar since it first tracked off of Africa on September 4th and passed just north of the Leeward Islands on September 9th. It then tracked into the Bermuda Triangle where it has done a large loop. Jose is in the process of finishing its dance in the Bermuda Triangle and will slowly track northwest over the next several days.

The risk of Jose’s impact on the U.S. had been relatively low (less than 20%) until the last 24 hours. With better long-range modelling, however, we can now get a clearer picture of what the end game might entail for Jose. In fact, currently the official National Hurricane Center (NHC) track puts a good chunk of the coastal Northeast just inside the “cone of uncertainty,” which means there is now a chance that Jose will directly impact areas from the NC Outer Banks to points north, including Cape Cod, later next week.

This is the American GFS Model Forecated Trend heights at the middle of the Atmosphere. Showing a trend of higher heights which means more blocking to the north of Jose’s track.

The key to the forecast is going to be just how strong and how far west the Atlantic ridge of high pressure is as Jose begins to turn north this weekend. Also, with the ridge of high pressure trending stronger north of New England next week, the general idea that Jose will escape out to sea is becoming more uncertain, given this large-scale atmospheric pattern. This could allow for Jose to track into New England versus turning east. So, once again, there is some long-range forecast drama to watch next week. My general feeling is the high pressure to the north looks to be stronger, which means the probability of landfall is now as high as 70% for parts of New England on Thursday of next week.

In terms of intensity, although the NHC is not forecasting Jose to become a major hurricane on its current path towards the East Coast of the U.S., I think there is a decent chance that Jose could become a solid Category 3 again before encountering cooler waters north of North Carolina.

As Jose tracks northward west it will first run into warmer than normal water before it tracks over cooler than normal waters.

These cooler waters will be a critical factor in how intense Jose becomes after Wednesday of next week.  Currently these sea surface temperatures of 23 C / 73 F are not very supportive of a hurricane.

Current surface water temperatures off the east coast of the U.S

This will likely result in a much weaker storm,  but it depends on how strong Jose can get earlier next week.  Right now a Category 1 hurricane impacting the East Coast next week can’t be ruled out, but it is unlikely.  There is a better likelihood of Jose becoming extra tropical at this point and could even slow and become a bigger rain maker late next week.

Next week I can provide more details about the possible impact once the track becomes more stable, but, at this time, big swells will be increasing along the East Coast which will cause beach erosion. As Jose tracks closer to the East Coast, the most likely scenario is that it will track just off shore, which would mean that the strongest winds on the right side of the storm would stay off shore, but coastal flooding could be an issue, as the winds possibly push water down Long Island Sound and against the New Jersey coastline later next week.

Main Development Troubles

Meanwhile, last night the NHC upgraded a tropical wave coming off of Africa to Tropical Depression (TD) 14. It will likely develop into Tropical Storm (TS) Lee later today and should eventually turn north to the open Atlantic. However, this should be watched more closely, as the general steering flow this year has indicated that these tropical systems are tracking closer to the U.S. because of the Bermuda High. To the west of TD 14 is an invest area labelled 96L which could become TD 15 or TS Maria at some point as it cruises west toward the Windward Islands later next week. Currently the NHC has a 50% chance of cyclone formation over the next two days, but a 90% chance of formation over the next 5 days.  It should be noted both Invest 96L and TD 14 will run into higher wind shear which could weaken the systems as they track westward this weekend. If the storms do last until early next week, expect Invest 96L to be close to the Windward Islands and TD 14 to be tracking northeast toward the Leeward Islands.  I am most concerned with Invest 96L at this time, because as it gets closer to the U.S Caribbean, we have seen this season that conditions are more conducive for East Coast impacts.

General ideas of track of current tropical systems into next week.

Regardless, this is simply a busy season, the likes of which we have not seen since 2012. It is important with all of the other news and distractions going on around the world and locally that we remain focused on hurricane preparedness and these future storm threats.