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Tropical Storm Barbara Discussion Number 4

Wiki-Hurricanes Forecast Center

2:00 PM PDT Sun Jun 30 2019

Barbara is not a particularly healthy tropical cyclone this afternoon. Visible satellite images show that the low-level circulation was partially exposed for a short period of time before new convective cells covered it. The cyclone continues to be affected by moderate levels of northerly mid-level wind shear, forcing most significant convection into the storm's semicircle. This is despite the fact that upper-level outflow is expanding in all directions. Regardless of the exposed center, Dvorak estimates have risen to at least T2.5/35kt from SAB and TAFB, as well as UW-CIMSS ADT. Furthermore, a series of ASCAT passes around 16z showed several 40kt wind barbs in the eastern and southern quadrants. Barbara's initial intensity is set at 40kt accordingly.

There remain questions surrounding the intensity forecast moving forward, although the overall philosophy remains the same. Moderate mid-level winds are still predicted to slacken, although perhaps not as quickly as indicated last night. Ocean temperatures are expected to hover around 27-28C through four days, while mid-level relative humidity values will become unfavorable shortly before that time. There is unanimous agreement between the ECMWF, GFS, SHIPS, and LGEM that Barbara becomes a major hurricane in about three days, with the ECMWF going further to Category 4 intensity. The two biggest uncertainties remain the storm's broad size, which may prolong the amount of time it takes for an inner core to form, and also the impacts of a convectively-coupled kelvin wave traversing the region. The large radius of maximum wind presents a net negative for Barbara and may allow intermittent periods of dry air entrainment. The kelvin wave presents an increased probability for rapid intensification once an inner core does form, however. The updated intensity forecast continues to show slow or steady development over the next day and a half, with more rapid intensification thereafter. A level off in strength and weakening is expected on days four and five as Barbara encounters cooler water and a more stable environment.

Barbara is moving on a straightforward west-northwest track, and this motion should continue over the next 72 hours as a mid-level ridge remains positioned over northern Mexico. By day four, models indicate that the storm should reach the southwest periphery of this ridge, and a more poleward motion toward the northwest may ensue. By day five, though, this ridge is forecast to extend westward and intensify, forcing Barbara on a more westerly course. Models are in good agreement regarding this forecast philosophy.

FORECAST MAX WINDS

INIT 30/2100Z 40 KT 45 MPH

12H 01/0600Z 45 KT 50 MPH

24H 01/1800Z 50 KT 60 MPH

36H 02/0600Z 65 KT 75 MPH

48H 02/1800Z 80 KT 90 MPH

72H 03/1800Z 100 KT 115 MPH

96H 04/1800Z 100 KT 115 MPH

120H 05/1800Z 85 KT 100 MPH

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