Atlantic Invest 92L Likely Depression

By: Dr. Jeff Masters , 8:08PM,GMT on July 21,2014

(By Steve Gregory - Substituting for Dr. Masters who is on Vacation.)

SPECIAL UPDATE

Latest VIS and IR imagery suggests INVEST 92L is now a Tropical Depression, though NHC has not yet ‘called it’.



Fig 1: Latest VIS image of INVEST 92 about 1,200 NM east of the Lesser Antilles.

The low level circulation near 11.1N / 43.5W (about 1,200NM east of the Lesser Antilles) appears ‘closed’, with significant, though weak convection noted within 25NM of the center, along the S-SE side of the center.



Fig 2: The 85Ghz microwave image from a pass earlier today indicates convection is located very close to the low level circulation which I believe supports designating this system as a Depression.

The quite small developing cyclone is moving westward at 18 Kts, and is embedded in a relatively moist environment with low wind shear (<10Kts). However, the system is still located over relatively cool SST’s, and this does not support strong convection. Until the system gets closer the CARIB in about 48 hours, where SST’s exceed 28ᵒC, it is doubtful the system will be able to intensify beyond a minimal Tropical storm.



Fig 3: The latest SST analysis in the vicinity of 92L indicates SST’s are significantly below the threshold needed for deep convection and intensification beyond minimal storm intensity.

The large scale global models do not have a handle on this small system, but the specialized Tropical Cyclone models, initialized at 18Z, forecast the storm to track towards the CARIB, reaching the eastern CARIB late in the day THU or by early Friday. The statistically based intensity models show the cyclone becoming a tropical storm by then, though the more reliable dynamical models are NOT forecasting the system to show significant intensification – and at this time, this seems like the most likely solution as wind shear and drier air are likely to be encountered by the time the cyclone approaches the CARIB.



Fig 4: The Early 18Z cycle model runs are little changed from the early morning runs, but now show the system reaching the CARIB a bit earlier, reflecting the relatively fast forward motion that should continue as long as there is no deep convection.



Fig 5: The more reliable dynamical models do NOT intensify the cyclone – and this seems to be the most likely solution as the system should encounter a more hostile environment by the time it reaches the CARIB.

Update on CAT 1 MATMO

The latest GFS model run shows MATMO moving somewhat faster than earlier progged, and the Typhoon should reach the eastern coast of Taiwan as a strong CAT 2 Typhoon around 00Z Wednesday.

The next full update will be Tuesday afternoon unless conditions in the Atlantic warrant an earlier posting. Steve Gregory