Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 3:51 AM GMT on November 19, 2013
Subtropical Storm Melissa formed over the central Atlantic today from a non-tropical area of low pressure. As of the latest NHC advisory, the following information was available on Melissa:
Wind: 60 mph, with higher gusts
Location: 30.3°N 54.7°W
Movement: NW at 8 mph
Pressure: 985 mb
The cloud pattern connected to Melissa is still decidedly non-tropical. While the outer convective bands about 100 miles south of the center seen earlier this evening have largely dissipated and convection has formed closer to the center, the cloud tops encompassing this new convection are not particularly cold given the high latitude of Melissa. TAFB furnished a satellite classification of 3.0 as of 0z. While this would normally portend surface winds of only 45 kt, the Dvorak technique only works for systems that are fully tropical, which Melissa is not. A recent AMSU microwave pass shows me that Melissa still lacks an inner core.
Figure 1. Latest infrared satellite image of Subtropical Storm Melissa. Image credit: NOAA's Satellite Services Division (SSD).
While scatterometer fixes have been somewhat patchy, the data I've been able to collect suggests that the radius of maximum winds has contracted compared to 24 hours ago, but Melissa is still embedded within a broader-scale cyclonic low over the central Atlantic, as denoted by surface and satellite observations. AMSU vertical temperature profiles indicate that Melissa is putting up a valiant fight in making the transition to a tropical storm, warming in the upper troposphere has been slow and perhaps unsteady. In addition, water vapor imagery and UW-CIMSS 200 mb vorticity data suggest that Melissa is still well-involved with a large upper-level low pressure system. The SHIPS model analyzed areal sea surface temperatures of only about 25.5C, which appears to be about 1.5C too cold given sea surface temperature maps. Hence, I have high hopes that Melissa will make the transition to a tropical storm on Tuesday, and while, not explicitly shown yet, there is a chance that the cyclone could briefly reach hurricane strength, perhaps up to about 70 kt; this would occur as Melissa moves underneath the axis of a narrow upper ridge forecast to develop over the system in about 24 hours. Subsequently, as the cyclone enters higher latitudes, moves over cold water, and experiences increases in vertical shear, weakening is anticipated. The current model guidance does not show an environment that really screams out "baroclinic forcing" to me, so a steady decline in intensity is expected even after the system becomes extratropical. There is the possibility that Melissa could become a non-convective remnant low at the 48 hour mark before it interacts with an upper-level trough moving off the eastern United States, but the timing and magnitude of this transition is difficult to predict.
Melissa still appears to be moving northwestward, but a turn to the north is expected to manifest very soon as a deep-layer trough moves off the east coast of the United States within the next 12-24 hours. Melissa is expected to move northward only briefly, as the trough will impart mid-level southwesterly flow to the cyclone and accelerate it northeast to east-northeast. The model guidance has no real conundrums except for the end of the period, when the GFS and ECMWF differ significantly on whether Melissa will continue eastward toward western Europe, or whether it will continue north into Greenland. My forecast track compromises the possibilities, lacking any reason to favor one scenario over the other, and is a little left of the current NHC prediction.
Due to the limitations of the track map on which I draw my forecast tracks, I am unable to furnish a forecast point out to day five.
Intensity forecast and positions
INITIAL 11/19 0300Z 30.3°N 54.7°W 50 KT 60 MPH
12 hour 11/19 1200Z 31.5°N 53.8°W 55 KT 65 MPH...TROPICAL
24 hour 11/20 0000Z 34.4°N 51.2°W 60 KT 70 MPH
36 hour 11/20 1200Z 37.1°N 48.2°W 60 KT 70 MPH
48 hour 11/21 0000Z 40.5°N 44.5°W 55 KT 65 MPH
72 hour 11/22 0000Z 45.1°N 40.0°W 50 KT 60 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 11/23 0000Z 50.7°N 41.0°W 45 KT 50 MPH...POST-TROPICAL/EXTRATROPICAL
120hour 11/24 0000Z 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
Figure 2. My forecast track for Melissa.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
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