Still Waiting on Invest 93L to Form into Tropical Depression

As of Wednesday morning, Invest 93L still showed signs of circulation but has yet to become a tropical depression. Shower and thunderstorm activity was fairly limited and it looked like dry air as well as increased wind shear from Tuesday was taking a toll on the disturbance. The enhanced satellite picture is not all that impressive looking.

Floater IR Enhanced to Water Vapor

One of the reasons for 93L’s struggles has been the dry air in its vicinity. The Saharan Air Layer is quite prominent in the central and eastern Atlantic. And while technically 93L is south of the SAL plume, it is evident that some of that dry air is becoming entangled in the system. However, as the disturbance works west-northwestward over the coming days, the atmosphere should moisten up some, and the dry air will become less of a problem.

Saharan Air Layer

Another issue for Invest 93L over the last 24-48 hours has been higher wind shear (on the order of 10-20kts over that time frame). The image below (courtesy the University of Wisconsin-Madison) shows a minima of wind shear, however, in the path of the disturbance. Thus this should become less of an issue for 93L to form tropically.

Wind Shear

In fact, the GFS model shows wind shear remaining fairly low for the next couple of days across the eastern Caribbean, which should allow 93L to form into a tropical disturbance in that time frame. Beyond that, shear does kick back up by later Saturday into Sunday across the western Atlantic.

GFS Wind Shear

One final issue for Invest 93L has been water temperatures. It’s still a little early in the year to see Cape Verde storms develop because water temperatures are marginal at best to support tropical genesis. However, as the disturbance moves closer to the Lesser Antilles, water temperatures begin to increase. In general, the warmer the waters, the better heat transport into the storm and thus the more likely the disturbance becomes a tropical depression.

Caribbean and Atlantic Water Temperatures

As mentioned above, with all these mitigating conditions becoming more favorable in the next 24 hours, tropical development is likely. In fact, the National Hurricane Center gives Invest 93L a 70% chance of developing into Tropical Depression Three by the end of the week. The question then becomes track of the disturbance. Most of our more reliable computer models are in agreement in the short term, pushing the potential storm into the northern Lesser Antilles by late Friday/early Saturday. Interests in the Lesser Antilles should monitor the disturbance closely.

Invest 93L Models

The question then becomes where does the storm go from there. Ultimately, this question will depend highly on the strength of whatever system forms. Model solutions range from a weaker storm that stays on a west-northwest path toward the east coast of Florida, to a stronger system that stays well out to sea. Luckily for us, this is still nearly a week out and the path will likely begin to become clearer over the coming days. Stay tuned for the latest!Invest 93L Models 2

Invest 93L Could Become Tropical Depression Three Tuesday or Wednesday; Interest in Lesser Antilles Need to Monitor

Invest 93L continues to organize Tuesday and a tropical depression could form later today or Wednesday. There is a slight hiccup in organization early Tuesday as convection isn’t quite as strong. This is due to 20-30 kt moderate shear. Upper level winds are a little less hostile Wednesday as the disturbance moves west northwest at 10-15 mph. There is also a bit more dry air southwest and north of the area of low pressure Tuesday. The area of low pressure is a bit more compact Tuesday and if convection deepens near its center mid-week Tropical Depression Three could form. The National Hurricane Center ups the chances of Tropical Depression to a high 70% by Thursday and 80% over the next five days so it’s only a matter of time.

Floater IR Enhanced

Floater IR Enhanced to Water Vapor

Computer models track Invest 93L west northwest through Thursday around a ridge of high pressure. Models bring it towards the Lesser Antilles, especially the Leeward Islands Friday or Saturday. Beyond that time frame models differ in the strength and future track so interest in the eastern Caribbean and even the Bahamas need to watch this one closely.

Invest 93L Models with Satellite

The 06Z GFS brings tropical storm Bertha over the Leeward Islands and Virgin Islands Saturday. If this solution is valid heavy rain and tropical storm force winds are possible over the weekend.

GFS MSL and Precip Rate

It took a few days but European model is a little more impressed with Invest 93L, especially in the short term. It depicts a weaker system but a faster moving system than the GFS. A weaker low would tend to track further west and have a greater impact on Puerto Rico and possibly Hispañola and the Bahamas. The 0Z Euro brings the disturbance to the northeast Lesser Antilles Friday night into Saturday. Hurricane Hunters are deck to investigate Invest 93L Thursday, if necessary.

ECMWF MSLP and Precip Rate

 

Invest 93L Better Organized Monday; The Lesser Antilles Need to Watch Disturbance Closely

The tropical wave southwest of the Cape Verde Islands (now Invest 93L) has gradually organized over the past 24 hours. Convection explodes just north of the ITCZ  Monday morning over a moist environment. Wind shear values are low over the disturbance and it may continue to get its act together. The National Hurricane Center raises the odds of Tropical Depression 3 or Tropical Storm Bertha forming to 30% by Wednesday and a high 70% chance by Saturday.  Many computer models are on board with tropical cyclone formation by mid work week.

Floater IR Enhanced

The extent of dry African air (the Saharan Air Layer) is mainly north and west of Invest 93L. The disturbance will stay mainly south of this stable air mass which will allow further organization in the coming days. Water vapor imagery shows Invest 93L thrives over warm moist south central Atlantic waters.

Floater IR Enhanced to Water Vapor

Early Monday morning computer models suggest a westward track in the coming days at 10-15 mph. Invest 93L will ride the perimeter of the Bermuda high parked over the north central Atlantic. By late work week into the weekend  it will drift northwest around the high. During this time it may approach the Lesser Antilles. Interest in the Lesser Antilles need to watch this one closely Friday into the weekend.

Invest 93L Models

The GFS insists Tropical Storm Bertha will pass close to the north Lesser Antilles Friday or Saturday. The 06Z run suggests a strong tropical storm will pass over the islands Saturday and drift northwest. The reliable European model is not overly impressed with Invest 93L and does not develop a tropical cyclone. The less reliable Canadian and NAVGEM do develop a closed low. It’s too early to even discuss a possible track beyond the weekend. Model trends will be watched closely this work week.

GFS MSL and Precip Rate

Eastern Atlantic Disturbance Still Disorganized; Slow Development Possible as Cape Verde Season Nears

The tropical wave that we’re watching in the eastern Atlantic is less organized Sunday. Convection is shallow and widely scattered. There are no signs of a defined area of low pressure forming.  Wind shear values are low but there is plenty of dry air north of the disturbance. By mid-week the environment is a bit more favorable for gradual development as the tropical wave drifts westward. The National Hurricane keeps the odds of Tropical Depression 3 or Tropical Storm Bertha forming at 0% over the next two days but 40% by Friday. There is plenty of time to watch this feature.

Floater IR Enhanced

August officially begins on Friday. It makes sense that at least some computer models hint at development in the Atlantic. During the third month of the Atlantic hurricane season we see the biggest increase in tropical activity as we approach the peak of season in mid September. Cape Verde season is in August and September. As the Bermuda high strengthens in the north central Atlantic it guides tropical cyclones into the Caribbean and up into the western Atlantic or Gulf. This is when the strongest named storms often form.

Tropical Hurricane Frequency Graph-WTVT

While the reliable European model isn’t on board the GFS, NAVGEM, and Canadian model suggest tropical cyclone development mid to late work week. The 06Z GFS develops Tropical Storm Bertha and brings it over the Lesser Antilles late Friday into Saturday. Again, it’s still early but worth watching.

GFS MSL and Precip Rate 2

Meanwhile it’s quite active in the east Pacific but there are no imminent threats to land. Tropical Depression Genevieve struggles with westerly wind shear and will dissipate over the open Pacific Sunday night or Monday. Tropical Storm Hernan strengthens south of Mexico and nears hurricane strength. It will dissipate over cooler waters as it battles hostile upper level winds mid to late work week. Low pressure between Genevieve and Hernan isn’t quite as organized Sunday due to westerly shear. It still has a medium chance of becoming a tropical depression this work week but will stay over the open Pacific.

Tropical Track Pacific 3

Watching Tropical Wave Near the Cape Verde Islands; Slow Development Possible

As the month of July winds down our attention closes in on the coast of Africa. Cape Verde season is just around the corner. Cape Verde season generally starts in August and continues through September. Our strongest named storms often form during this time. There is plenty of time for tropical waves to eventually reach hurricane strength. They thrive over warm waters as moisture builds along the ITCZ. On average two Cape Verde hurricanes form each season.

Hurricane Special-Cape Verde Hurricanes

Right on cue a healthy tropical wave just south of the Cape Verde Islands is worth watching. Development, if any, will be a slow process. Wind shear values are at a low 5-10 kts Saturday and the most widespread dry Saharan air is well north of the tropical wave.The National Hurricane Center gives it a 20% chance of becoming a tropical depression or named storm (Bertha) by Thursday. There is plenty of time to watch this complex of thunderstorms as it moves westward in the coming days.

Eastern Atlantic IR Enhanced

Not all computer models are on board with the development of this feature.  Models like the GFS do suggest an area of low pressure may form mid-week between the Lesser Antilles and the Cape Verde islands. If the tropical wave stays far enough south to avoid the deepest dry African air it may organize during this time.

GFS MSL and Precip Rate

The graphic below shows the extent of the Saharan Air Layer courtesy of the University of Wisconsin. Notice convection along the ITCZ is a little more defined than it was just a weeks ago. This is a sign of moisture building as more tropical waves move off of Africa into the south central Atlantic. There is still plenty of dry air across the central Atlantic, Caribbean and Gulf which inhibits overall tropical cyclone development.

splitEW

Precipitable water or moisture values look to stay highest along the ITCZ into mid to late work week. That is the purple color on the graphic below. The yellow and blue-green color indicate drier air across the north central Atlantic and into parts of the Caribbean.

Precipitable Water

It’s busy in the eastern Pacific. Genevieve is now a Tropical Depression. It struggles will hostile upper level wind and will dissipate well southeast of Hawaii this work week. Tropical Depression 8E is no threat to land south of Mexico. It will likely become Tropical Storm Hernan later this weekend as it heads northwest. An area of low pressure could be forming between Genevieve and TD 8E. This could briefly become TD 9E tonight before upper level winds rip it apart.

Tropical Track Pacific 2

A Return to Quiet Conditions Across the Atlantic

As Tropical Depression Two dissipated on Wednesday, the Atlantic returned into relative peacefulness. A look at the enhanced satellite imagery shows a couple tropical waves. The first, near the Lesser Antilles, contains the remnants of T.D. Two which has become little more than some scattered thunderstorms with gusty winds. The second tropical wave, sitting about halfway between the Windward Islands and Cape Verde Islands, shows just scattered convection at this point with no center of circulation. No tropical development of this wave is expected at this point.

Eastern Atlantic IR Enhanced

Across the Gulf, temperatures have cooled off a bit in the last couple weeks, and now sea surface temperatures are running below average across much of the basin, which is usually where we look for tropical activity at this point in the season.

SST Caribbean Anomalies

Meanwhile, the eastern Pacific looks to get back going again. We are monitoring two areas of interest. The first (circled in red) has shown strong signs of circulation and the NHC is giving it an 80% chance of development in the coming days. Meanwhile, the second area of interest (circled in yellow) hasn’t shown much outside of some scattered convection and is only given a 10% chance of development in the next 2 days. However, environmental conditions will become more favorable beyond that time frame for development, and therefore the NHC ups the chances of development in the next 5 days to 50%.

Floater IR Enhanced

We are still watching the potential for El Nino as we head into the dog days of summer but so far, we have seen mainly neutral conditions. It is obvious by looking at sea surface temperatures across the Pacific that temperatures are running above average, even well above average in places. However, the atmosphere has yet to ‘line up’ with these anomalies. Nonetheless, El Nino is still expected to develop. The latest from the Climate Prediction Center gives a 70% chance for El Nino to form by later this summer, and an 80% chance to form by Fall/Early Winter. Obviously, the earlier El Nino forms, the more of an effect it would have on our tropical season. We’ll continue to watch the latest developments on its potential formation.

SST Global Anomalies

Tropical Depression Two Dissipates East of the Lesser Antilles

Dry air and increased upper level winds take a toll on Tropical Depression Two and it dissipates at 11 AM. The former small Tropical Depression is nothing more than a swirl of clouds with very shallow disorganized convection. Barbados and parts of the Windward Island will see at least a few tropical downpours later today and tonight but this won’t be a significant rain event with dry air in the vicinity.

Floater IR Enhanced

It’s common for convection to drop off a bit during the overnight hours. At midnight look how much deeper and compact convection is with former Tropical Depression Two. Westerly shear also increased overnight as the minimal tropical cyclone combated drier air.

Floater IR Enhanced 2

The biggest reason for T.D. Two’s demise is the amount of dry air in play, some of which is a direct result of the Saharan Air Layer (SAL). With the dry air surrounding the depression, it has essentially ’choked off’ the storm.

Floater 1 WV

This is also a sign of the time of year. As we get later into the season, there tends to be less dry air present across the Atlantic and the moisture influx into these storms tends to win out. During the third week of July from July 21-31 only 49 named storms formed in the Atlantic Basin from 1851-2013. Notice most of these formed in the Gulf or western Atlantic with fewer formation points in the south central Atlantic.

MyFoxHurricane Google Earth

Wind shear, which has been quite high for much of the season thus far, will ramp back up along the remnants of T.D. Two’s path. As depicted in the model image below, wind shear will be moderate just off to the west of the struggling disturbance which will also cause further weakening to the convection.

GFS Wind Shear

 

Tropical Depression Two Hangs On; Will Struggle With Dry Air

Tropical Depression Two remains a small minimal tropical cyclone Tuesday morning as it heads rapidly westward. Convection deepens a bit but this should be short-lived as it encounters dry stable air by tonight. This dry air and increasing upper level winds will lead to dissipation by early Thursday, if not sooner. Officially as of 11 AM Tropical Depression Two becomes a remnant low Wednesday night east of Barbados. Leftover moisture will bring scattered showers and thunderstorms to the Lesser Antilles and eventually Puerto Rico by the weekend. This won’t be a significant rain event.

Floater IR Enhanced

trackmap_storm1

Water vapor imagery clearly shows abundant dry air in the mid-levels of the atmosphere directly in the path of Tropical Depression Two. It stands no chance later this week. None of the relialble computer models forecast anything more than a minimal tropical storm.

SE WV

Another obstacle for Tropical Depression Two is increasing upper level winds. The 06Z Tropical WRF Model shows 15-30 kt northeasterly shear over the tropical cyclone Wednesday night. These values are moderate but with dry air in its path the storm will really struggle.

wrf_atl_shear_15

Regardless if Tropical Depression Two survives when it reaches the Lesser Antilles Thursday some tropical downpours are expected. The GFS model shows 1-2″ is possible for the Windward Islands through Thursday afternoon.

ECMWF-Precip Acc

Tropical Depression Two Forms in South Central Atlantic; Will Be Short-Lived

Tropical Depression Two forms Monday evening between the Lesser Antilles and the Cape Verde Islands. Convection deepens today as it tracks westward and it gains tropical depression classification. This is a minimal system with max sustained winds of 35 mph and  pressure estimated at 1012 mb. Tropical Depression Two faces a lot of obstacles in the coming days and should be short-lived. This isn’t a climatologically favor spot for tropical cyclone development this time of year. Dry air from the Saharan Air Layer (SAL) makes it difficult for systems to tropical waves and weak named storms to survive the track across the south central Atlantic.

Floater IR Enhanced

While the environment associated with the second tropical depression of the season is moist currently it will be encompassed by dry, stable African air in the coming days. This is mainly why none of the reliable computer models forecast a strong system. It’s also why the National Hurricane Center dissipates Tropical Depression Two by Thursday afternoon if not sooner.

Caribbean WV 

Water temperatures climb into low to mid 80s in the central Caribbean but there are still some luke warm reading east of the Lesser Antilles. Tropical Depression Two will struggle with dry air over these marginally warm waters.

Caribbean and Atlantic Water Temperatures

Interest in the Lesser Antilles should keep an eye on Tropical Depression Two but right now impacts look minimal.

trackmap_storm1

 

Eighth Week of Atlantic Hurricane Season Begins; Matmo Now a Typhoon East of the Philippines

The eighth week of the Atlantic season begins Sunday. While the Atlantic Basin is generally quiet there are signs of a bit more moisture building in the coming days/weeks. It’s common to ease into hurricane season with limited named storms in June and July. By late July into August activity typically starts to pick up and healthy tropical waves moves off of Africa. Climatologically the second named storm forms on August 1st and the first hurricane forms on August 10th. Hurricane Arthur formed in early July over warm gulf stream waters.

Climatology July

Climatology August

Scattered showers and thunderstorms continue in the wake of a stalled front along the northern Gulf coast. Weak low pressure east of the Mid Atlantic region continues to move northeast away from the U.S. Also a trough of low pressure stirs up convection over the Bahamas and Cuba.

Southeast Satellite-Radar Weekend AM

The Atlantic and Caribbean are a little more active but officially the National Hurricane keeps the entire Atlantic basin quiet for the next five days. Wind shear is still moderate to high but upper level winds aren’t quiet as hostile as they have been in recent weeks.  One tropical wave in the central Caribbean brings heavy rain to Puerto Rico and scattered convection to Cuba. This tropical wave interacts with moderate shear. A healthy tropical wave between the Lesser Antilles and the Cape Verde Islands sparks scattered convection. By mid work week it rides the perimeter of the Atlantic ridge into stable Atlantic waters which should inhibit significant organization. It is worth keeping an eye on although it poses no major threats.

Eastern Atlantic IR Enhanced

If tropical waves hold together in the south central Atlantic the atmosphere may continue to moisten. The graphic below shows forecasted precipitable water values per the GFS model into Friday. It suggests moisture levels may build along the ITCZ as tropical waves roll off Africa. The purple and red colors indicate deeper moisture. This is what we’d expect as we head into August and especially September.

Precipitable Water

Remnants of Typhoon Rammasun continue to bring heavy downpours to southeast China, Vietnam and Laos. Winds are much lighter Sunday. Typhoon Matmo is a minimal typhoon west of the Philippines but the southwesterly flow around the tropical cyclone brings soaking rains to parts of the Philippines. It will strengthen as it heads northwest in the coming days and could bring hurricane force winds and catastrophic flooding to Taiwan early Wednesday EDT.

Floater IR Enhanced

Tropical Track Pacific