Tropical Storm Nate Forecast/discussion 1:
Tropical storm Nate’s satellite appearance has only changed slightly since this morning, with the appearance of a sheared tropical cyclone evident with the center nearly exposed on the northeast edge of an area of deep convection. A recent microwave pass and air-force recon confirm this, with the center clearly displaced from the somewhat banded convection to the southwest of the center. Nate is nearly stationary at this time.
Nate’s track forecast is interesting. At the moment,ridging is in place to the north and to the east of the cyclone, allowing for very little movement. The current motion estimate from the NHC advisory is a SSE drift at about 2 knots. Over the next couple of days, most models attempt to drift the upper low associated with Lee’s remnants farther south into the Ohio/Tennessee Valleys, weakening ridging to the north of Nate. However, ridging should remain in place over the Caribbean to the east of the storm, allowing for a slight increase in forward motion, generally to the north, in the near term.
How far north Nate can get in the near term will be key, as the troughing from Lee’s remnants will only get as far south as the central Gulf of Mexico. For example, the 12z GFS has Nate moving north tonight at a few knots faster than the ECM, and in a few days has Nate far enough north that ridging cannot build back to the north as quickly when Lee’s remnants fill and move east, which would allow Nate to get north into the central Gulf and possibly threaten the northern Gulf coast as the GFS shows. However, the ECM does not bring Nate as far north nearly as quickly in the near term, and in the end begins to lift the trough over the southern/eastern US before Nate can get caught in the accelerated flow on the southern edge of the trough. This allows ridging to build back in north of Nate, allowing the cyclone to turn to the west and make landfall near Tampico Mexico in about 72 hours. Out of the 12z guidance, the CMC, NOGAPS, UKMET and ECM ensembles all agreed with this scenario. The GEFS mean was not as far north as the op GFS, but did not bring Nate inland as far south or as fast as the aforementioned guidance. ATCF track guidance agrees with this track forecast fairly well, however many models are slower than all of the globals (excluding the GFS), however many of these same ATCF models are GFS based. Given this, will ride the 12z ECM/ECM ensembles hard for this forecast, and will give the GFS and GFS based models little weight. Will show landfall near Tampico Monday morning.
As for the intensity forecast, Nate is currently dealing with some northeasterly shear. However, an upper level anti-cyclone is forecasted to build over the storm over the next 12-24 hours, causing the shear that is already decreasing to become favorable for further development. The 12z GFS and ECM models both showed Nate deepening steadily from Friday morning through Sunday. Nate is over fairly warm sea surface temperatures and will move overfairly high heat content waters over the next couple of days. While there is some pretty dry air to the northwest of Nate, it should become less of a problem as shear relaxes. Given this, will show steady intensification through landfall. Will follow the ATCF guidance closely (a tad stronger than the middle of the road), as most models show steady intensification through landfall. Nate still has to become vertically aligned and work out some dry air before it can explosively develop, so will not show rapid intensification in the forecast.
Initial…19.7N, 92.3W…60 knots, TS
24 hours (18z Friday)…20.2N, 92.3W…70 knots, Cat 1
48 hours (18z Saturday)…21.7N, 93.8W…80 knots, Cat 1
72 hours (18z Sunday)…22.1N, 95.7W…90 knots, Cat 2
96 hours (18z Monday)…22.0N, 97.9W…85 knots, Cat 2…Inland.