Igor's Future Not Clear Cut
Tropical Storm Igor has formed in the eastern Atlantic Ocean near the Cape Verde Islands from a strong tropical wave disturbance that rolled off of Africa. However, Igor is having a rough start. To see what I mean, lets first review the synoptic history of Igor:
Tropical Storm Igor
Dates: September 8 to Present
Maximum winds: 45 mph
Minimum pressure: 1005 mb
Synoptic situation: Igor originated from the sixth in a series of strong tropical waves that emerged into the Atlantic tropics from western Africa in late August and early September. On September 6, the aforementioned tropical wave entered the Atlantic with an expansive but disorganized area of storm activity. A study of satellite animation suggests that a rather strong storm cluster toward the western portion of the wave on the 7th led to a low pressure spin with well-organized storm bands by early on the 8th, located just south of the Cape Verde Islands. Persistent organization on satellite imagery coupled with a satellite scan of winds suggested that the low had quickly become Tropical Storm Igor by that late morning.
As Igor came into being, a rather strong storm flare off the coasts of southwestern Mauritania and northwestern Senegal developed, perhaps from the remaining eastern portion of the tropical wave. This led to the rapid formation of yet another tropical low pressure spin just northeast of Tropical Storm Igor later on the 8th. Subtropical ridging to the north began steering the tropical storm westward, with the forward speed slowing to a stall early on the 9th as the tropical storm was tugged into a Fujiwhara interaction** with the neighboring tropical low to the northeast. Storm relative easterly shear over Igor increased as the forward speed had fallen behind upper easterly wind speed induced by the deep-layered ridge and the outflow of the tropical low.
Color-enhanced infrared satellite image of Tropical Storm Igor in the eastern Atlantic tropics on September 8 next to a tropical low pressure center to the northeast it was interacting with.
** A Fujiwhara interaction is an interaction when two low pressure spins get really close to each other. Because the flow around a low pressure spin is cyclonic (counter-clockwise in the northern hemisphere), the two low pressure spins orbit each other cyclonically in a Fujiwhara interaction.
In summary, the problem with Igor is it has struggled during an interaction with another tropical low pressure center located just to its northeast. If Igor was much stronger than the tropical low, it would have no problem getting rid of it and becoming the dominant system (just like recently how much stronger Hurricane Earl was able to destroy weaker Fiona with wind shear produced by its outflow). Two things could kill Igor (1) Easterly shear, which is caused because Igor has stalled around while doing the above mentioned Fujiwhara interaction. Stalling in this location is bad for Igor because the deep-layered ridge to the north is producing a steady stream of upper easterly winds. If you have upper easterly winds over a stationary tropical storm, then the storm clouds get sheared westward away from the tropical storm center, which would kill the tropical storm. (2) As Igor tries to absorb (or "eat") the other low pressure today, it may itself degenerate into a broad area of low pressure that lacks a well-defined center. This is because the minimum pressure value of Igor is not much lower than the minimum pressure of the other low, so the two lows might just melt together into a disorganized system. If Igor was much stronger, than its much lower minimum pressure would have an easier time sucking up the other weaker low pressure.
In lieu of all this, I am predicting right now that Igor in the short-term will weaken to a tropical depression or dissipate.
After that, its possible (although I am not officially predicting this now) that the depression or remnants of Igor could strengthen into a much stronger system down the road. Granted that we will have warm waters and low shear in the future with this system, the only reason that wouldn't happen is because of lots of dry air currently seen in water vapor imagery between 40W to 65W, and between 15N and 25N.
Another interesting thought. Lets say scenario (2) above happens in a manner that Igor's remnant low and the other low melt together into a disorganized system. I wonder if that disorganized system were to then organize and develop into a tropical cyclone, would that tropical cyclone be renamed Igor? Its possible that it wouldn't be renamed Igor because technically that new tropical cyclone is a product of Igor's low mixing with another low. It'll be interesting if that scenario ever happened.
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