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Tropical Storm Barbara Discussion Number 6

Wiki-Hurricanes Forecast Center

2:00 AM PDT Mon Jul 01 2019

Barbara's satellite representation continues to improve this morning. Despite microwave passes earlier last night showing a system that was not well stacked vertically, with convection displaced to the east of the low-level center, the CDO has expanded in the past hours, particularly westward over the location of the low-level circulation. As a result, it is presumed that the system has become vertically better organized. The banding in the southwest sector continues to persist. Scatterometer data from the 0452z ASCAT-A pass shows an expansive area of 45 kt winds east of the center. A 06z Dvorak estimate from TAFB came in at T3.5/55kt, which appears to be a good estimate for Barbara's intensity given the intensification trend since then. As a result, Barbara's initial intensity has been raised to 55 kts this advisory.

Barbara continues on a west-northwest track and is expected to track in the same direction for the next for the duration of the forecast period. Barbara still seems to be dealing with a bit of westerly shear, but this is forecast to decrease to marginal levels over the next day or so, although it may increase briefly late in the forecast period around day four due to the influence of an upper-level trough. Sea surface temperatures in the vicinity of the storm are a warm 29C for the moment, but they will begin to gradually cool by day 2, yet remain sufficient to support the storm, but they will become marginal by day 4. The storm will have plenty of moisture for the next few days as well before dry air begins to increase significantly. In this situation though, the main factor is SSTs which depend upon the exact track the storm will take. Models have disagreed to what extent the northward component of Barbara's motion will be, although the main outlier, ECMWF, has come more in line with the rest of the models as of the 00z runs. Unfortunately, with a westerly shift forecast near the end of the period (with the westerly shift of the subtropical ridge), even a degree of meridional displacement may result in a wildly different actual intensity depending on whether it ends up over marginal 26C waters or waters too cool to support the storm.

SHIPS and LGEM continue to produce stronger outputs and RI indices have increased. Given this current trend, the forecast has been adjusted upward and steady strengthening is forecast for the next three days, at which point Barbara will be approaching category four strength. Beyond this point the intensity should level off or begin to decrease as conditions become less supportive of a major hurricane and by day 4 the combination of factors becoming increasingly unfavorable will result in rapid weakening.

FORECAST MAX WINDS

INIT 01/0900Z 55 KT 65 MPH

12H 01/1800Z 65 KT 75 MPH

24H 02/0600Z 75 KT 85 MPH

36H 02/1800Z 90 KT 105 MPH

48H 03/0600Z 100 KT 115 MPH

72H 04/0600Z 110 KT 125 MPH

96H 05/0600Z 100 KT 115 MPH

120H 06/0600Z 70 KT 80 MPH

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