The synoptic (large-scale) pattern remains key in how quickly a trough (dip in the jet stream) moving through the east is able to exit the United States. Latest indications are trending for the potential of a faster exit of this trough which could potentially leave Irma behind as high pressure in the upper-levels of the atmosphere builds in (behind the departing trough) to the north of Irma.
Latest Global Ensemble Forecast System (GEFS) Spaghetti Tracks:
Latest Canadian Ensemble Prediction System (GEPS) Spaghetti Tracks (image courtesy WxBell):
Latest European Ensembles:
The European Ensembles (image below) still show a decent spread in outcome of exact track with some members (little red “L”s) over Cuba and others northeast of the Bahamas by Sunday September 10th at 12Z (8AM EST).
The Evolution of the Upper-Level Pattern its Impact on Steering Irma:
– The image below shows the past 7 model runs (forecast outputs for Sunday evening, September 10th) from the Global Ensemble Forecast System (GEFS).
– Notice the shift southwestward in potential location of Irma at this time frame as latest indications (subject to change) indicate that the 500-mb trough may slip off of the New England coastline with a ridge of high pressure building to the north of Irma. It’s too soon to know exactly where Irma will track as we are still more than 10 days out.
Global Forecast Ensemble System (GEFS) Trend Model:
- This image shows the past 9 forecast trend outputs for the same time: Sunday morning on September 10th
- Notice the shift to the southwest in clustered location of the GFS Ensemble members (various possible locations of where Irma could be located on Sunday morning).
- Bottom Line: Uncertainty remains very high and this is not unusual for ten days out (as we all know with forecasting the tracks of a nor’easter during the winter months here in the Mid-Atlantic)