BMS Tropical Update 9/15/2017 12 PM CDT

By: - September 15th, 2017

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.

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