Showers and thunderstorms associated with an areas of disturbed weather about 850mls WSW of the Cape Verde Island has become a little better organized during the past few hours.This systen has a medium chance(50%) of developing within the next 48hrs as it moves westward or west northwestward at 10 to 15mph.
Elsewhere in the North Atlantic, the Caribbean Sea and the Gulf of Mexico, Tropical Cyclone formation is not expected during the next 48 hours.
Tropical Atlantic Wide Infrared Satellite Image:
USA National Weather Service Forecast
6:00 am EST on July 29, 2014
For the North Atlantic...Caribbean Sea and the Gulf of Mexico:
Satellite data indicate that an area of low pressure located about
1000 miles west-southwest of the Cape Verde Islands is becoming
better defined. The associated shower and thunderstorm activity
continues to gradually organize, and a tropical depression could
form during the next day or so while the system moves westward or
west-northwestward at 10 to 15 mph.
* Formation chance through 48 hours...high...near 70 percent.
* Formation chance through 5 days...high...80 percent.
48 Hour Forecast – Favorable Environmental Conditions For Tropical Development
The tropical disturbance halfway between the Lesser Antilles and the African coast continues to become better organized this morning, and it seems likely that this feature will become the third tropical cyclone of the season. The environmental factors that have thus far inhibited development, dry air and wind shear, appear to be weakening -- as such, Tropical Depression Three may develop later today.
The system is expected to track generally west-northwest over the next couple of days with a gradual turn to the northwest late in the week. This will place it close to the Leeward Islands by Saturday, though the exact path remains uncertain. The disturbance is expected to strengthen at a modest pace, likely becoming "Bertha" over the next day or two. It is difficult to say how strong this feature may become, however, though the latest intensity guidance suggests some potential for the disturbance to become a hurricane before affecting the Leeward Islands.
Looking ahead further, the track that the system takes will be largely dependent on how strong it is... with a weaker system moving more westward and a strong system more likely to turn away from the eastern U.S.
Elsewhere across the basin, there are no concerns for tropical development.
120 Hour Forecast – Favorable Environmental Conditions For Tropical Development
Invest 93L Will Likely Become A Tropical Depression Sometime Later Today & Then Strengthen Into Tropical Storm Bertha Sometime On Wednesday As It Tracks Towards The Lesser Antilles; Everyone Across The Central & Northern Lesser Antilles, Virgin Islands & Puerto Rico Should Closely Monitor Invest 93L As Tropical Storm Conditions Seem Likely This Weekend
Rob Lightbown of Crown Weather Services
Tuesday, July 29, 2014 7:05 am
Invest 93L was located near 9.7 North Latitude and 37.3 West Longitude or about 1550 miles to the east of the Lesser Antilles this morning. Satellite imagery showed that this system continues to become better organized with curved banding noted in satellite loops. I maintain that Invest 93L is probably already a tropical depression, if it isn’t, it’s very, very close to becoming one just based on satellite data.
An analysis of environmental conditions around Invest 93L indicates that upper level winds are favorable for strengthening for at least the next few days. Wind shear values around and ahead of Invest 93L shows that there is currently 20 knots of shear impacting this system, however, these values drop to 10 knots just to the west of this system. In addition, it appears that the amount of dry air over the central and eastern Atlantic continues to decrease. This tells me that the environmental conditions continue to become more favorable for development across the central and eastern Atlantic and this trend is expected to continue throughout this week leading to the strengthening of Invest 93L/Bertha.
The various track guidance with Invest 93L indicates that they seem to agree that this system will continue tracking westward today and tonight before turning to the west-northwest sometime on Wednesday with an impact on the central and northern Lesser Antilles during the day on Saturday followed by an impact on the Virgin Islands and Puerto Rico from Saturday night into Sunday. It is noteworthy that the track guidance has shifted a little to the southwest with its forecast track of Invest 93L especially as we get into Saturday and Sunday. This likely means that the forecast of the ridge of high pressure over the western Atlantic may be stronger than previously forecast leading to potential impacts to the Bahamas and a threat to the US East Coast next week. More on that later in this discussion.
The latest intensity guidance suggests that Invest 93L could be a upper end tropical storm or even a hurricane when it impacts the central and northern Lesser Antilles and the Virgin Islands this weekend. This increasing trends in the intensity guidance is something that needs to be monitored closely.
Here are my latest thoughts: Invest 93L is well on its way to becoming a tropical depression by later today and then likely Tropical Storm Bertha sometime on Wednesday. I agree with both the track and intensity guidance with Invest 93L and think that this system may direct impact the central and northern Lesser Antilles, including the islands of Dominica, Guadeloupe, Antigua, St. Martin and Anguilla as at least a moderate to upper end tropical storm and very possibly a borderline hurricane during the day on Saturday. So, expect winds of 50 to 80 mph, heavy rainfall with amounts of 2 to 5 inches and very rough seas during Saturday. The remainder of the Lesser Antilles will receive a glancing blow in terms of some gusty winds and bands of heavy rain during Saturday.
From there, it seems quite possible that the Virgin Islands and Puerto Rico will be impacted by this system from Saturday night through Sunday with upper end tropical storm and possibly hurricane conditions possible, especially across the Virgin Islands from Saturday night through Sunday.
For Those Of You Across The Central and Northern Lesser Antilles, Virgin Islands & Puerto Rico: Please watch this system extremely closely and start going through your hurricane preparedness checklist to make sure you have all your supplies ready. It is looking likely that tropical storm and even hurricane conditions may impact you from Saturday into Sunday.
Looking ahead to next week, the trends in the global model guidance suggests that the high pressure system over the western Atlantic may be strong enough to allow for a track that impacts the Bahamas and possibly threaten the US East Coast. Current analysis reveals that there is currently a large weakness in the ridge of high pressure to the north of Puerto Rico with a trough of low pressure expected to remain in place over the eastern United States from today through this weekend. It seems that the global models want to pull this trough of low pressure back to the west and lift it out as a ridge of high pressure builds westward in its place. If this occurs, then a track that brings it close to the Bahamas around Monday and Tuesday of next week and off of the US East Coast around Wednesday and Thursday of next week would be possible. This is something that is very far out in time, but it is something that will need to be watched closely.
Elsewhere, another area of disturbed weather is now located over the far eastern Atlantic just to the east of Invest 93L. This disturbance will be monitored closely, however, immediate development is unlikely and none of the global models forecast development of this system. The reasons why are because the upper level winds are expected to be marginally favorable for development from today right into this weekend. Also, the outflow from Invest 93L will likely put a cap on any significant development.
Invest 93L Information:
Model Track Forecast:
93L in Eastern Atlantic Growing More Organized
2:43 PM GMT on July 28, 2014
An area of disturbed weather located near 10°N, 33°W at 8 am EDT Monday, about 500 miles southwest of the Cape Verde Islands, was designated Invest 93L by NHC early Monday morning. This disturbance is a more serious threat than Tropical Depression Two of last week, and has the potential to develop into a strong tropical storm before reaching the Lesser Antilles Islands on Friday or Saturday. Visible satellite loops on Monday morning showed that the disturbance had only a modest amount of spin, but infrared satellite images showed that the system's heavy thunderstorm activity had increased significantly since Sunday. Wind shear was light, 5 - 10 knots, which should aid development. Ocean temperatures were decent for development, about 27.5°C. Water vapor satellite loops showed that the atmosphere was reasonably moist in the area, though a large area of dry air lay a few hundred miles to the north.
Figure 1. Analysis of the Saharan Air Layer (SAL) made at 8 am EDT Monday July 28, 2014 using data from the Meteosat-9 satellite. Dry, dusty air was present from the coast of Africa westwards across the tropical Atlantic, but was located well to the north of tropical disturbance 93L. Image credit: University of Wisconsin CIMSS/NOAA Hurricane Research Division.
Figure 2. MODIS true-color image of 93L from approximately 9:30 am EDT July 28, 2014, when the storm was about 500 miles southwest of the Cape Verde Islands. The disturbance was embedded in the Intertropical Convergence Zone (ITCZ), the band of heavy thunderstorms that circles the globe in the tropics. Image credit: NASA.
Forecast for 93L The 12 UTC Monday forecast from the SHIPS model predicted that wind shear will remain low to moderate, 5 - 15 knots, for the remainder of the week, aiding development. Sea Surface Temperatures (SSTs) will cool a bit to 27°C on Tuesday and Wednesday, which will tend to slow development. Two of our three reliable models for predicting tropical cyclone genesis, the GFS and UKMET models, predicted in their 00Z Monday runs that the disturbance would develop into a tropical depression by Thursday. Several of our less reliable models, the NAVGEM and Canadian models, also predicted development. The only reliable model that did not predict development was the European model, which historically has had the highest incidence of failing to predict development when development actually occurs. The fact that two out of three of the reliable genesis models predict development bolsters the odds that development will actually occur. In their 8 am EDT Monday Tropical Weather Outlook, NHC put the 5-day odds of development at 70%, up from their 40% forecast from Sunday.
All of the models predict that the disturbance will continue due west or west-northwest at 10 - 15 mph for the next five days. The UKMET is the fastest of the models, predicting that the disturbance will arrive in the Lesser Antilles Islands on Friday evening. The GFS is slower, predicting a Saturday morning arrival in the islands. Once the disturbance crosses west of about 55°W longitude on Thursday, ocean temperatures will warm to about 28°C, which should aid development. Dry air to the north will likely interfere with development late in the week, and we will have to see if the moderate levels of wind shear forecast to occur over the tropical Atlantic will be capable of driving this dry air into the core of the system, disrupting formation. The disturbance may also have trouble disentangling itself from the Intertropical Convergence Zone (ITCZ), the band of heavy thunderstorms that circles the globe in the tropics, which lies just to the south of the disturbance. Clusters of thunderstorms in the ITCZ may compete for moisture and energy, slowing development of the disturbance.
The long-range fate of 93L remains highly uncertain, and will depend upon exactly how far south the center ends up consolidating when the storm develops. Most of the 20 members of the 06Z Monday run of the GFS ensemble model (which runs the GFS model at low resolution 20 times with slightly different initial conditions to show a range of possible outcomes) showed the disturbance missing the U.S. East Coast and recurving out to sea next week; four of the members showed 93L hitting the Southeast U.S. coast. Most of the members of the 00Z Monday run of the European ensemble model showed 93L moving into the Eastern Caribbean on a more southerly trajectory without recurving.
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