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By: wxchaser97 , 8:09 AM GMT on June 30, 2013
Tropical Depression 4E
A new tropical depression has formed in the Epac, just a couple days after Cosme dissipated. TD-4E was previously invest 96E which originated as a disturbance in the monsoon trough. The disturbance acquired a decent surface circulation and was organizing convection over the past couple days. The only problem was it was still embedded in the monsoon trough. Two nights ago and early yesterday, it broke away and lost a good amount of its convection. The diurnal cycle also played a factor in this. As time went on the circulation became fully closed and convection increased over the center again. At the 8pm PDT, invest 96E was designated as TD-4E due to the increased organization. TD-4E continues to strengthen tonight as it heads toward the north. A Central Dense Overcast (CDO) region has developed over the center and there is a few curved bands showing up on the latest microwave pass. Satellite images show solid outflow associated with TD-4E. This is because of the anticyclone developing over TD-4E which is ventilating the system. This is shown on the global models and UW-CIMSS wind analysis. SAB, TAFB, and SSD-ADT are all at 2.0 with UW-CIMSS ADT at 2.4. All of these numbers still support tropical depression strength, but they have been increasing throughout the day. With the recent organization trends and a favorable environment, I expect TD-4E to become a tropical storm pretty soon. The latest storm info, satellite image, and microwave image can be found below.
11:00 PM PDT Sat Jun 29
Location: 14.3°N 103.0°W
Moving: N at 10 mph
Min pressure: 1004 mb
Max sustained: 35 mph
Forecast for TD-4E
TD-4E has a favorable environment for strengthening, possibly rapidly, for the next few days. TD-4E has a moist atmosphere with very warm waters and low wind shear. As mentioned above, the depression has an anticyclone overhead. This should act to shield the system from any harmful wind shear. The latest SHIPS diagnostic message has wind shear staying at or below 10kts for the whole forecast period. This is definitely favorable for intensification. The only threat for shear, and this would be late in the forecast period, is by the weakening/displacement of the anticyclone. The GFS and NAVGEM somewhat show this, the system will already be on a weakening trend when/if that happens. TD-4E is situated over very warm ocean waters and is expected to remain over very warm SST's for several days. The SHIPS analysis indicated SST's over 29C for the next 2 days while staying favorable for the next 4-5 days. There is also modest ocean heat content values in this area for the next several days. They are expected to drop to near zero in 3-4 days, along with a drop in SST's themselves. 700mb-500mb relative humidity values are in the 70% realm and should remain between 60%-80% for the entire forecast period. This means TD-4E shouldn't have much issues with dry air. In fact, the SHIPS analysis gives TD-4E a 52% chance of Rapid Intensification (RI) of 25kts. This is a similar situation to Cosme, but closer to Mexico and TD-4E is a lot smaller. Because of the smaller size 04E can feel the effects of its environment quicker than a larger system. This is good as long as it can build an inner core, which it is trying to do so. If TD-4E can get a defined inner core, then RI is definitely possible and hurricane strength is likely. My thinking is steady intensification for the next 12-24hrs and then quicker intensification as the inner core gets defined. I am positive that the depression will get to hurricane status even though the NHC doesn't think so. To be honest, I'm not totally sure why they don't forecast it becoming a hurricane. I know intensity models don't show it becoming a hurricane but with the environment TD-4E is situated in a hurricane is likely. I am forecasting a peak of 80kts in about 3 days. This is considerably higher than global, dynamical, and statistical models but it is reasonable with the conditions it has to work with. It is possible it becomes stronger than expected if RI does occur or a little weaker if strengthening is slower to occur. After about day 3, TD-4E should begin to weaken due to the cooler waters and no heat content of the higher latitude water of the Epac. I don't expect TD-4E to become post-tropical or a remnant low during the forecast period. There is a chance that this intensity forecast busts but at the moment I don't think it will.
TD-4E is currently moving to the north and this general motion is expected to persist for a little while longer. 04E is situated between an upper-level-low to its northwest and another one in the gulf. This has created a weakness that is pulling the system generally to the north. The flow should remain like this for about the rest of the day. As the system gets farther north, it will begin to get influenced by the strong ridge centered over the Four-Corners region. The ridge will turn the depression to the west-northwest and then west over the coming days as it becomes the dominate steering mechanism. This will bring TD-4E and its impacts away from the Mexican coast and not threaten any other areas. As the system gets embedded in the cyclonic flow it will be taken out to sea. Most of the global, dynamic, and statistic models keep 04E from making landfall. It should be noted that some models do take 04E inland, but right now the westerly flow should be able to turn it away before making landfall. It will be close to the coast whether or not TD-4E makes landfall. Heavy rain, gusty winds, and higher waves can be expected along and near the south-central Mexican coast from the outer bands of the system. Since TD-4E will be passing very close to the coast, Mexico has issued tropical storm warnings and watches, which are seen below, for parts of the Mexican coast. All the necessary tropical cyclone preparedness actions should be taken in those areas that will be affected.
Warning and watch info:
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE SOUTHWEST COAST OF MEXICO FROM PUNTA SAN TELMO TO MANZANILLO
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE SOUTHWEST COAST OF MEXICO FROM NORTH OF MANZANILLO TO LA
INIT 30/0800Z 30 KT 35 MPH
12H 30/1800Z 40 KT 45 MPH
24H 01/0600Z 50 KT 60 MPH
36H 01/1800Z 60 KT 70 MPH
48H 02/0600Z 75 KT 85 MPH
72H 03/0600Z 80 KT 90 MPH
96H 04/0600Z 70 KT 80 MPH
120H 05/0600Z 50 KT 60 MPH
I'll have a new update on TD-4E sometime today along with an update on July Atlantic development potential and the rest of the season. Have a great night/morning.
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