Maria a Threat to the Northern Lesser Antilles, Puerto Rico, Hispaniola, and the Bahamas

Maria forecast/discussion 2 (update to forecast 1):

Tropical Storm Maria remains highly disorganized, with pulsing convection noted north of the low level circulation on IR Satellite loops and microwave images. Because of the center being displaced from the convection, Maria has weakened some today as I expected last night. Maria is still heading just a tad north of due west, at 275/15, and has gained very little latitude since yesterday.

Track forecast reasoning remains essentially unchanged, although will have to be adjusting slightly south/west due to yesterdays day 1 forecast busting too far to the north. Maria is on the southern periphery of a subtropical ridge over the central Atlantic and will begin over the next 48 hours gradually turning more WNW and then NW with time as ridging to the north of the cyclone weakens over the western Atlantic due to Lee’s remnants over the OH/TN Valleys and due to the upper level westerlies being farther south than normal over the western Atlantic due to a positive NAO.

However, given Maria will remain weak in the short term and given the cyclone has tracked farther left than anticipated in the near term, a track close to or over Puerto Rico and near but likely still north of Hispaniola will be forecast, which is farther south than yesterday’s forecast. In addition, a track much closer to the central Bahama’s will be shown. The GFS and its ensembles show Maria tracking north and being picked up by troughing associated with Lee’s remnants before they pull out causing the system to recurve well off the US east coast. However, the ECM and its ensembles slow Maria down in the mid range and narrowly allow Maria to escape before troughing pulls out of the eastern US. While landfall is still not likely in my opinion, the 12z Euro ensembles show troughing along the east coast at day 6, in association with a (brief) -NAO/+PNA. However, the ensembles allow a strong Pacific jet to weaken the western US ridging after this, and show the pattern becoming much more zonal over the eastern US. Should Maria slow down more than expected this weekend into early next week, it is an outside possibility that Maria gets caught up in weak steering currents off the southeast coast. However, this would require Maria to significantly slow down which appears unlikely given there is a fairly fast flow surrounding the ridge that is steering it, and would also require ridging to build back in over the eastern US days 7-10. While both are possible, it is unlikely both will happen at the right times to bring Maria much farther west (into the southeastern US).

As for intensity, moderate shear and dry air are still causing problems for Maria, with convection exhibiting a pulsing pattern. The convection is also displaced from the center of circulation. These problems are expected to continue plegging the tropical storm over the next couple of days. With some decent low level ridging north of Maria, the steep pressure gradient produced may help to continue generating some TS force winds on the northern side of the circulation, assuming some convection continues to fire. So, will maintain Maria as a minimal TS for the next 48 hours. Thereafter, the global models attempt to weaken the shear over Maria and the GFS, CMC, and NOGAPS attempt to develop an upper level anti-cyclone over Maria, just as the system also begins to slow some. All of these global models and the vast majority of the hurricane models show some intensification starting about 48 hours out. The 12z Euro was not so optimistic. The GFS, CMC, NOGAPS and about 2/3rds of the ATCF guidance suggest a cyclone nearing or exceeding hurricane stregnth by day 5. Given that at the upper levels the Euro looks favorable once Maria approaches the Bahamas, will bring Maria up to a minimal hurricane by day 5, despite the ECM not showing much intensification.

Forecast track/intensity:

Initial (0z Friday)…13.2N, 53.6W…35 knots, TS
24 hours (18z Friday)…13.5N, 59W…35 knots, TS
48 hours (18z Saturday)…16N, 65W…35 knots, TS
72 hours (18z Sunday)…19N, 69W…45 knots, TS
96 hours (18z Monday)…22.2N, 72.7W…55 knots, TS
120 hours (18z Tuesday)…25.1N, 76W…65 knots, Cat 1

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