TAOI 07-24-2010

Summary: Tropical Storm Bonnie was downgraded to a Tropical Depression at 2100UTC yesterday while over the western Florida peninsula. While TD Bonnie has since emerged into the Gulf, no re-intensification has occurred, and the National Hurricane Center has discontinued all tropical storm warnings for the Gulf coast. The upper level cold low in the Gulf of Mexico has continued to move westward and is now located just off the Texas coast. Elsewhere in the tropics, upper level diffluence south of 2 upper level lows- the Gulf of Mexico low, and a second low- located just NE of Cuba, is supporting continued convection. At 1200 UTC, the National Hurricane Center had a low probability of development associated with the Caribbean convection, but this has since been discontinued. A tropical wave, formerly PGI-18L, is located over the Leeward and Windward Islands, while PGI-19L continues to slowly progress westward. The Newfoundland low has moved eastward, bringing the front with it, while a subtropical high has remained fairly stationary. A second subtropical high has developed to the south of the front at 50W, 30N.

Forecast:
The primary features of interest within the IPEX/PREDICT/GRIP domain are the Bonnie, the convection south of Cuba and Hispaniola, convection over the Bay of Campeche, and a tropical wave over the Leeward and Windward Islands (ex-PGI-18L). PGI-19L is also of interest, though currently located outside of the domain. Likewise, the cold low east of Newfoundland and accompanying front continue to propagate westward. While the low and accompanying front are not expected to impact any systems of interest in the near future, they continue to represent a break in the large scale North Atlantic flow. While the focus remains on Bonnie today, it will shift to other features tomorrow as Bonnie moves inland.

At 1500UTC, Tropical Depression Bonnie was located at 86.7W, 28N. As has been the case throughout Bonnie’s life, it is largely under the influence of an upper level cold low, now located off the Texas coast. For the last few days, Bonnie has been located in an area of moderate shear. However, shear has increased today, in part due to the combined influences of the upper level low and an upper level ridge over the eastern US. Largely due to the high shear, no re-intensification of Bonnie has occurred. While a burst of convection occurred near the center at 0400UTC today, it was ripped apart by shear, and the center is now almost entirely devoid of any deep convection. Convection is still occurring in bands to the north west of the center of circulation. Precipitable water remains high around Bonnie’s location, however water vapor imagery shows that Bonnie is becoming separated from the moisture in the Caribbean. Weak upper level divergence and lower level convergence associated with the convection to the northwest of the center of circulation are present in CIMSS analysis, however lower level vorticity has decreased in magnitude since yesterday, and vorticity is not well stacked in the 850-500mb layer. The 12Z model guidance is in very good agreement that no further development of Bonnie will occur. Even the statistical-dynamical models which had favored development throughout the life of the storm no longer predict any intensification. Therefore, the current intensity of 30 kts is expected to persist until it makes landfall later today near the Louisiana, Mississippi border.

Elsewhere, the global models do not favor the development of any other systems within the next 48 hours. The ECMWF maintains the convection in the southern Caribbean for a day or two before dissipating it. The GFS does develop an area of high 950mb vorticity in the Bay of Campeche, however it is limited spatially, slightly smaller than Bonnie’s vorticity signature, and immediately moves inland. Pouch tracking does not favor the immediate development of PGI-19L. In fact, the ECMWF doesn’t even track it. As a result, no development of any other systems is expected within the next 48 hours.