The tropical wave we began discussing last week was designated as invest 98L a couple of days ago and has made its way to the Caribbean where it continues to become better organized:
It is important to note that a low-level circulation has not yet developed, making the forecasts uncertain. However, there are a couple of scenarios we can discuss. First up, you can see the spread in the models below, with some models quickly developing the system and turning it north toward Hispaniola and others keeping it weaker and sending it further west:
This split in the road for 98L's future track is also demonstrated nicely by the Google AI model that has performed so well this season:
The GFS is all in on the north turn and has most of its members turning north over Hispaniola likely due to the fact it strengthens it much faster than any other model:
Whereas the Euro keeps most of its members moving slowly through the Caribbean where it gets trapped for a few days and doesn't make the turn north yet:
This is due to the system getting trapped between two upper-level highs with very little in the way of steering for 98L:
With the potential for a large, slow-moving system, the rainfall forecasts are quite extreme as demonstrated by the Euro Ensemble rain forecast. A large area of 10"+ is depicted over the Caribbean, including parts of Haiti, Jamaica, and the Dominican Republic. That much rain over the mountainous terrain of those islands would cause drastic damage:
While we can't completely rule out US impacts from 98L, the odds at this time are low. A wall of shear from the subtropical jet will act as a sort of barrier for the time being:
However, if the system stalls out long enough and gets far enough west, the pattern currently being forecast for near Halloween could open the door for US impacts as a strong upper-level low could pull the system north. How far west it gets will determine if the US will be impacted:
Regardless, interests in the Caribbean should continue to monitor the forecast. Remember, until there is a closed circulation, models will continue to struggle with the forecast and it will be a few more days until we have a clearer picture.