9/25/19 Tropical Storm Karen Update – a hype-free look at what we know

Author: || Published: 9/25/2019 at 11:26am
9/25/19 1130am CDT – North Atlantic Infrared imagery // Courtesy: College of DuPage Meteorology

It seems like Tropical storm Karen is getting a lot of attention from folks during the last 48 hours. It is understandable. The last few years has featured multiple landfalling tropical systems – some more potent than others. And a lot of people have been affected – directly and indirectly – by these storms.

With Karen being the “K” storm, it brings back bad memories along the northern Gulf Coast for some people in Louisiana, Mississippi, and Alabama.

That is also understandable.

But Karen is – by far – not even the best looking storm in the Atlantic. Lorenzo is a very healthy looking system of the coast of Africa. Karen is a pretty beat-up Tropical Storm north of Puerto Rico. Looks aren’t everything, I know. But I say that the highlight that if you see a map (like the one above) floating around and see the big tropical system in the Atlantic – don’t assume that is Karen.

Karen isn’t looking healthy at the moment.

But let’s take a look at what we know about Karen and the forecast for the storm – with no hype and no unnecessary extrapolations.



From the National Hurricane Center

SUMMARY OF 1100 AM AST…1500 UTC…INFORMATION
———————————————–
LOCATION…21.7N 64.9W
ABOUT 240 MI…385 KM NNE OF SAN JUAN PUERTO RICO
MAXIMUM SUSTAINED WINDS…45 MPH…75 KM/H
PRESENT MOVEMENT…N OR 360 DEGREES AT 15 MPH…24 KM/H
MINIMUM CENTRAL PRESSURE…1003 MB…29.62 INCHES

Five-day forecast for KAren from the NHC // Courtesy: nhc.noaa.gov

Tropical Storm Karen Discussion Number 14
NWS National Hurricane Center Miami FL AL122019
1100 AM AST Wed Sep 25 2019

Karen is still having a tough time establishing and maintaining a well-organized structure. The deep convection which developed over the center earlier this morning has since collapsed, leaving a ragged and disorganized cloud pattern. In addition, a sizable outflow boundary moving away from the eastern part of the circulation suggests that there is dry air within the vortex. The initial intensity is being held at 40 kt, pending possible scatterometer data later this morning and a reconnaissance flight
this afternoon.

The initial position is a little difficult to locate, but the best estimate of the current motion is 360/13 kt. Karen is moving northward between a mid-level high centered over the central Atlantic and a mid- to upper-level low located just east of the Bahamas. This low is expected to slowly retrograde westward, with ridging developing over the western Atlantic by day 3. This change in steering will cause Karen to turn northeastward during the next 48 hours but then make a clockwise loop once it is blocked by the ridge. After day 3, the ridge should force Karen to move west-southwestward. Most of the track models agree on this general scenario. There is some latitudinal spread on days 4 and 5 after the loop occurs, with the HWRF being the most notable outlier by not showing much of a westward motion. The consensus aids, however, have remained fairly steady, and therefore there was no compelling reason to make any significant changes compared to the previous track forecast.

Except for the possibility of dry air in the circulation, it’s not quite evident why Karen has not been able to sustain organization. Still, the cyclone is expected to move beneath an upper-level anticyclone during the next 24-48 hours, and if the shear does indeed decrease, then some strengthening would be expected. There continues to be a dichotomy among the intensity models, with the dynamical models (including the GFS and ECMWF) keeping the cyclone weak while the statistical-dynamical models still show intensification through days 4 and 5. It’s difficult to ignore what’s being shown by the global models, since there must be something in the environment that they’re deeming to be negative for continued strengthening. The best course of action at this point is to maintain a steady intensity after 48 hours, but it should be noted that what is shown in the official forecast still lies above the ICON intensity consensus and the HCCA corrected consensus aid.




Model Data

The model data on Tropical Storm Karen is far from a “lock” with respect to intensity.

9/25/19 12z Intensity model guidance for Tropical Storm Karen // Courtesy: Tropical Tidbits

However, it is good to see that most models keep the system as a Tropical Depression or Tropical Storm through the next 72 hours. That is encouraging for people concern about eventual impacts tot he United STates of the Bahamas. Obviously, rain is always a concern with every tropical system, but seeing that the intensity of the winds will be below Hurricane Strength can offer a little comfort that – at the moment – the models don’t see any kind of Rapid Intensification.

9/25/19 SHIPS RI model guidance for Tropical Storm Karen // Courtesy: nhc.noaa.gov

Even the SHIPS model that handles the Rapid Intensification guidance is showing reasonably lower numbers for any kind of quick ramp-up in intensity.

And that is despite the environment become a bit more (not a lot) favorable in the coming days.

9/25/19 model gudiance for Tropical Storm Karen // Courtesy: http://rammb.cira.colostate.edu

The guidance shows that deep-layer shear is going to diminish and sea-surface temperatures will remain about the same. If you only look at the data above, the only thing that would get in the way of extra development could be some dry air getting entrained within the system.

But, of course, that isn’t the only data available.

So, why is there no explosive development?

It is complicated, but it may have to do with the remnants of Jerry, the developing ridge (behind a front) in the Atlantic, and the amount of stretching caused by the two.

Plus, a weakness that may develop between two ridges of high pressure of the east coast of the US that may coax Karen north before reaching land.

A couple of looks at some model data – surface, 850mb, 500mb – for Tropical Storm Karen // Courtesy: Pivotal Weather

The above graphic shows a weak front between the subtropical ridge in the South and the developing ridge near Bermuda. That front may open a gap between the two ridges to coax Karen north – or it may not. It is a bit too early to tell, but it is worth noting that, within the current available data, the two ridges are shown up at 500mb, but are less and less pronounced as you drop closer to the surface. And, at the same time, a weak front is more pronounced, indicating a difference in the two airmasses.

What does all that mean for Karen? Unfortunately: TBD.

However, this is a good indication that we are starting to get a better idea about what pieces of the puzzle are in play for KAren’s eventual journey.




Thoughts from other Meteorologists

Occasionally I like to add in thought from other meteorologists. The community of forecasters – from research to broadcast to NWS – is rich with varying degrees of experience and knowledge. It is always nice to be able to digitally shoulder-tap others for their thoughts.

What can you do right now?

Keep tabs on teh forecast, that is about it. Double check your Hurricane Preparedness kit to make sure you are full-up on supplies. But other than that, there isn’t much else to be done at the present time.




Author of the article:


Nick Lilja

Nick is former television meteorologist with stints in Amarillo and Hattiesburg. During his time in Hattiesburg, he was also an adjunct professor at the University of Southern Mississippi. He is a graduate of both Oregon State and Syracuse University that now calls Houston home. Now that he is retired from TV, he maintains this blog in his spare time.