Masters student in tropical meteorology at FSU. Raised in Alaskan blizzards, but drawn toward tropical cyclones by their superior PGF.
By: Levi32 , 4:23 PM GMT on June 13, 2009
Tropical Tidbit from 12:30pm EDT Saturday, June 13, 2009:
The persistent upper trough is still sitting in the NW Caribbean this morning, causing atmospheric instability and diffluence aloft generating showers/thunderstorms in Jamaica, Cuba, Haiti, and the Caymans. The main trough energy has lifted out and can be seen as a shortwave trough northeast of the Bahamas. The tail part left behind over the NW Caribbean will start closing off into a cut-off ULL (upper-level low) today and tonight. Meanwhile, an equally persistent surface trough in the western Caribbean along 81W continues to enhance shower activity west and south of Jamaica. Looking at the satellite shot you can see the huge build-up of heat in the form of convection over the east Pacific and southern Caribbean (see figure 1).
None of the global models do much with the Caribbean trough anymore. The NOGAPS takes a very weak trough NW into the Gulf of Mexico, and the 06z GFS finally got its timing right and took a weak low into the southern Yucatan in 72 hours. The ECMWF also shows a very weak low east of Belize in 72 hours. The area of 30-knot wind shear still over the southern Caribbean will start to lift northward tonight as the ULL over the NW Caribbean closes off and starts to back SW towards Guatemala. By monday the ULL will be in the EPAC and an upper high will build over the western Caribbean, providing ventilation and a low-shear environment. A weak surface low may try to form along the trough axis during this time and move NW near Honduras and Belize, but significant development is not expected. I will continue to monitor the area for any changes.
Elsewhere....a tropical wave along 63W is moving through the windward islands bringing showers, mostly concentrated in Trinidad and Tobago. This wave has weakened since yesterday and is currently embedded within a dry air mass, but in 2-3 days it will be in the western Caribbean where the environment will be much more hospitable. With all the heat sitting in there all it takes is one wave to take advantage of it, and therefore I will keep an eye on it.
A cold front sitting off the eastern seaboard is expected to continue to sit there for the next several days. The GFS and CMC are forecasting a sub-tropical low to form along the tail-end of this front off North Carolina in 3-4 days in the low-shear void between the subtropical jet and the polar jet. This area will be watched for mischief as well.
We shall see what happens!
Figure 1. The IR satellite image from this morning shows a lot of convection over the EPAC and southern Caribbean, indicating the build-up of heat in this part of the tropics. A lot of this is due to the MJO upward motion pulse which is moving into this area right now. This heat and moisture will be slowly advancing northward into the western Caribbean and southern Gulf of Mexico over the next 2 weeks, and these areas will have to be watched for tropical trouble during that time.
Figure 2. GFS 72-hour forecasted total precipitation. The ULL and surface trough in the western Caribbean are expected to generate 1-3 inches of rain for Cuba, the Caymans, Jamaica, and central America over the next 3 days.
Caribbean Visible Satellite: (click image for loop)
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.