Hurricane Earl affecting the NE; Fiona weakens; ex-Gaston likely to regenerate; 99L worth watching; possible cyclogenesis in the BOC in a few days

Tropical Update

Earl has begun to move over cooler waters and increasing vertical wind shear, thus it has begun to weaken and is barely clinging on to hurricane status. Latest satellite images of Earl conclude that the system is quite large, latest data from the reconnaissance aircraft suggests that tropical storm-force winds expand a large area. So, even though Earl continues to weaken, tropical storm-force winds will likely be felt across a large area of New England, the Canadian Maritimes, and points northward. Earl continues to move generally towards the NE/NNE as it is embedded in the southwesterly/south-southwesterly steering flow ahead of the mid-latitude trough currently recurving the system. This motion will likely continue for another day or two before it gets absorbed by a larger and more powerful extratropical low pressure area. Nonetheless, the areas under a watch and/or warning should closely monitor the progress of Earl and heed any evacuations requested by local officials.

Figure 1. An Aqua MODIS satellite image of Hurricane Earl earlier today around 17:50 UTC or 1:50 PM EDT. 

Tropical Depression Fiona continues to weaken as it interacts with cooler SSTs and 20-25 knots of northeasterly shear thus forcing convection to the southwest of the circulation. Continuous weakening is anticipated tonight, and based on the current lack of convective organization, deactivation tonight seems imminent. Bermuda should still monitor the progress of Fiona as it may bring some rough seas and gusty winds, but not anything more.

The remnants of what once was Tropical Storm Gaston has been showing signs of organization throughout the entirety of the day. Latest satellite imagery reveals that a large and circular convective cluster has developed atop the circulation of ex-Gaston. This indicates that conditions are slowly becoming more conducive for development. Although upper level winds are a marginal 10-15 knots in the vicinity of ex-Gaston, the dry and stable air that surrounds the system particularly to the west and north has proven to be the largest impediment on organization. Ex-Gaston is currently embedded in the mean easterly flow of the subtropical ridge. Although steering currents are relatively weak at the current (which is what is causing the slow motion), the steering currents should slowly begin to strengthen as a mid to upper level ridge over the central Atlantic begins to develop. This should cause ex-Gaston to begin to move towards the west, possibly even to the WSW, at a more rapid rate. The system should then enter into the Caribbean, whether it makes a trek across the Caribbean or tries to recurve due to a weakness in the subtropical ridge remains highly uncertain. No matter what type of track it does take in the Caribbean, interests along the Lesser and Greater Antilles should closely monitor the progress of ex-Gaston. As of 8pm EDT the NHC gave ex-Gaston a 60% chance of re-developing into a tropical cyclone in the next 48 hours, I do now believe that these chances are a bit higher, near 70%. 

A vigorous tropical wave accompanied by a broad area of low pressure (99L) has been showing slow signs of organization. Upper level conditions are currently marginally conducive for further organization, due to this I agree thoroughly with the current percentage given by the NHC (30%), however, global models do indicate that upper level conditions should become favorable. This system is currently moving towards the NW, and more likely than not,  will recurve as most global models along with dynamical model plots indicate. Interests along the Cape Verde islands should monitor the progress of 99L as it may bring torrential rainfall along with gusty winds.

Taking a look into the future, several global models such as the GFS, ECMWF, and CMC have been developing a low pressure area in the BOC from what seems to be TD-11E which is currently located in the Gulf of Tehuantepec in the eastern Pacific ocean. I will closely monitor this area as it is rather likely that we may see some tropical cyclogenesis in the BOC since conditions appear relatively conducive for anything to spin up in that area. The African wave train will also be monitored as it appears to be picking up yet again.

Elsewhere, tropical nor subtropical development is anticipated through Saturday

Figure 2. Infrared satellite image of the tropical Atlantic.

Next Update

I will have another update tomorrow.

Have a great evening!

MiamiHurricanes09