WRUF Weather

Season’s fourth storm could develop soon; could also dissipate soon after

A vigorous tropical wave emerged off the west coast of Africa Monday, and the National Hurricane Center began labeling it as Invest 98L.  As of late Monday evening, it was given a “medium” chance of developing into the season’s fourth named tropical storm, which would be called Dorian.  While conditions appear marginally favorable for development over the next 48 hours, the potential storm would have an uphill battle to stay alive across the central Atlantic by week’s end and poses no immediate threat to the United States (or any land mass, for that matter).


  • Moderate chance of developing into T.S. Dorian Tuesday or Wednesday
  • Whatever forms would likely dissipate in central Atlantic by end of the week
  • No immediate threat to any land mass, and certainly not the U.S.

Invest 98L is currently located several hundred miles southeast of the Cape Verde Islands and is moving west-northwest at 15 to 20 mph.  Satellite data suggests there is a weak cyclonic signature to the thunderstorm activity, but a closed surface low has not formed yet.  A second area of thunderstorm activity and lower pressure was also noted over land in western Africa, also moving west at around 20 mph.



Convection, or thunderstorms, are forecast to continue developing with Invest 98L as the system moves south of the Cape Verde Islands on Tuesday.  A consensus of forecast data does suggest a closed area of low pressure would likely develop near this convective activity, likely resulting in tropical cyclone formation late Tuesday or Wednesday.  Environmental parameters thereafter are not as conducive for tropical cyclone development or strengthening over the waters of the central Atlantic.  In fact, there are several forecast models that show 98L (or Dorian) dissipating by week’s end well east of the Leeward Islands and Caribbean.

Projected wind shear near 98L early Thursday morning. The red areas indicate high wind shear.

First of all, water temperatures in 98L’s path are still just a bit tool cool over a large area of the eastern Atlantic.  The most-recent data shows sub-80°F temperatures east of -40°W and north of 12°N.  Secondly, the presence of a large area of dry desert air (commonly referred to as the Saharan Air Layer, or SAL) will most-certainly be ingested into whatever circulation does form, likely suppressing robust thunderstorm development near the system’s center, which is a necessary component for tropical cyclone maturation.  The third (and likely final) hurdle 98L would have to navigate around would be the projected wind shear that forms near the system by mid-week.  A strong ridge of high pressure has been planted over the Atlantic, spanning the entire ocean for several weeks.  Strong northeast winds around this ridge would likely interfere with the system’s overall health and could cause it to dissipate entirely by Thursday or Friday.  Even if 98L (or Dorian) were to survive into the weekend, several long-range forecast charts suggests a turning to the northwest and possible re-curviture out to sea.  Speculation on any type of end result such as this, though, is a bit premature until we know if we will have a named storm or not.  

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