1:00 PM | *Atlantic Basin tropical activity may experience another surge during the first half of November*

A “red flag” during the tropical season for the possibility of enhanced activity is the formation of strong high pressure ridging over the Northeast US or southeastern Canada. This kind of pattern can lead to convergence across the tropical Atlantic and “open the door” for tropical activity to impact the Gulf of Mexico, Caribbean Sea or southwestern Atlantic Ocean. Map courtesy NOAA, tropicaltidbits.com

Overview

Since the middle of last week, two separate tropical systems attained tropical storm status adding to the year’s total number of named storms to 15 in the Atlantic Basin. Neither one of these most recent tropical storms, Nadine and Oscar, are a threat to the US mainland as the first one has already dissipated and the second is destined to push out over the open waters of the western Atlantic Ocean. There are signs, however, that tropical activity in the Atlantic Basin may be very well get boosted again as we push into the first half of November.

The Madden-Julian Oscillation (MJO) is a metric used by meteorologists to track the movement of a disturbance across the tropics. Depending on its position, it can lead to enhanced tropical activity over, for example, the Atlantic Basin. Signals including the MJO, point to more favorable atmospheric conditions for tropical activity during the first half of November across such regions as the Gulf of Mexico, Caribbean Sea and southwestern Atlantic. Plot courtesy NOAA, ECMWF

Madden-Julian Oscillation (MJO)

Meteorologists track an oceanic-atmospheric phenomenon known as the Madden-Julian Oscillation or MJO which affects weather patterns across the globe. Unlike El Nino or La Nina which are stationary features in the equatorial Pacific Ocean, the MJO is an eastward moving disturbance of clouds, rainfall, winds and pressures that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days, on average. The MJO was first discovered in the early 1970s by Dr. Roland Madden and Dr. Paul Julian when they were studying tropical wind and pressure patterns. 

The MJO consists of two parts or phases with one being the enhanced rainfall (convective) phase and the other being the suppressed rainfall phase. The location of the convective phases is often grouped into geographically based stages that are numbered 1-8 by scientists. The location or phase of the MJO can be tied to specific weather patterns in different parts of the world depending on the time of year. The MJO creates favorable conditions for tropical cyclone activity which is why it is important to monitor during the Atlantic Basin tropical season.

Latest computer forecast models suggest the MJO will move into a more favorable activity for tropical activity in the Atlantic Basin during the very end of October and first half of November. As an example, the latest Euro model forecast of the MJO features movement into “Phase 7” and then “Phase 8” as the calendar turns to November and these locations are typically associated with increased upward motion over places like the Gulf of Mexico, Caribbean Sea, and southwestern Atlantic Ocean.

Tropical Storm Oscar, the 15th named storm of the season, will move in a northeasterly direction during the next few days and pose little threat to the US mainland. Map courtesy NOAA/NHC

500-millibar height anomalies

Another signal for the possibility of enhanced tropical threats in the Atlantic Basin for early November comes from the latest model forecasts of “500-millibar height anomalies”. During the tropical season, a “red flag” is raised whenever model forecasts suggest strong high-pressure ridging will form over places like southeastern Canada or the Northeast US. This kind of positioning of an upper-level ridge often leads to enhanced convergence in the tropical Atlantic and can “open the door” for tropical waves to develop “underneath the ridge” and then move westward towards the SE US, Gulf of Mexico or Caribbean Sea. Indeed, the latest forecast by, for example, the ensemble version of the NOAA GFS model features strong high pressure ridging over the NE US and southeastern Canada by the first week of November.

Bottom line...stay tuned...there may be some more tropical mischief to deal with before attention can turn to the rapidly approaching winter season.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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