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Tropical Storm Barbara Discussion Number 2

Wiki-Hurricanes Forecast Center

2:00 AM PDT Sun Jun 30 2019

The tropical cyclone in the East Pacific has continued to organize since the previous advisory. While the extent of exceptionally deep convection has shrunk over the past few hours, thunderstorm activity has become more positioned about the low-level circulation. It is a sprawling system, with multiple spiral bands in the southern semicircle. Water vapor imagery shows that while upper-level outflow is expanding in all directions, there is a very evident band of northerly winds under the outflow layer imparting some moderate wind shear on the system. Nonetheless, a 0447z ASCAT pass showed several 35kt wind barbs to the east of the storm's center and countless barbs at or above 30kt. Therefore, I have high confidence in upgrading the system to Tropical Storm Barbara.

The overall forecast philosophy remains the same as the last advisory. While moderate mid- to upper-level winds are impacting the tropical storm in the near term, this wind shear is expected to relax over the next 24 hours, becoming favorable for at least steady intensification thereafter. Ocean temperatures are expected to remain more than sufficient for intensification over the next 72 to 96 hours, and mid-level relative humidity values should remain favorable until that time as well. The biggest impediment beyond today is likely to be Barbara's large size, which may deter quick intensification until an inner core is established. As far as available modelling is concerned, the GFS, ECMWF, and HWRF are now in pretty good agreement regarding both the timing of strengthening, although they differ in terms of absolute peak. Therefore, the intensity forecast has been adjusted to better fit those models, which includes raising the storm's top winds and also indicating slight weakening on day five. It should be noted that a convectively-coupled kelvin wave is currently traversing the equatorial East Pacific. Previous research has shown that these waves increase the odds of rapid intensification, with their effects maximized two days following the passage. It would not be surprising if Barbara strengthened quicker and more than currently indicated.

Barbara has been wobbling west to west-northwest today, and this motion is expected to continue for the next 96 hours or so as the storm is steered by an expansive mid-level ridge over northern Mexico. With time, this ridge is expected to propagate westward into the East Pacific. This should coincide with Barbara gaining vertical depth, resulting in a turn more toward the west on or around day five, and perhaps a more southerly component beyond the forecast period.

FORECAST MAX WINDS

INIT 30/0900Z 35 KT 40 MPH

12H 30/1800Z 40 KT 45 MPH

24H 01/0600Z 45 KT 50 MPH

36H 01/1800Z 55 KT 65 MPH

48H 02/0600Z 65 KT 75 MPH

72H 03/0600Z 80 KT 90 MPH

96H 04/0600Z 95 KT 110 MPH

120H 05/0600Z 90 KT 105 MPH

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