It’s looking more and more likely that July 2017 will wrap up with no additional named storms in Atlantic Basin. Only one named storm formed this month, Don. It was shredded apart by wind shear in the Caribbean and dry air kept it short-lived and weak. Dry air has a firm grip on the Caribbean and central Atlantic Tuesday, and there are no areas of interest for at least the next 5 days.
A fresh batch of Saharan air is situated over the south central and eastern Atlantic near Africa. All four tropical waves between the Lesser Antilles and Africa will stay disorganized due to this feature. The graphic below is courtesy NOAA/the University of Wisconsin.
Fast forward to the weekend and the Saharan Air Layer (SAL) remains quite active, especially in the Main Development Region. Dry, dusty stable air sticks around through at least next Sunday. Long-range computer models are pretty quiet. The 12Z Euro attempts to close off weak low pressure late next work week as a tropical wave approaches the eastern Caribbean. The latest GFS shows absolutely no tropical cyclone formation for the next 2 weeks+. Activity will likely ramp up at some point in August. Once dry air erodes, there is the potential for stronger storms to thrive off of warm sea surface temperatures.
The eastern Pacific is especially active. 5 named storms have formed over the past two weeks. On Tuesday there are three named storms: Hurricane Hillary, Hurricane Irwin and Tropical Storm Greg. All three will stay over the open Pacific waters. Greg could dissipate by Wednesday but Irwin and Hillary strengthen. Due to proximity, Hurricane Irwin and Hurricane Hillary will interact with, and possibly rotate around each other later this work week. This is called the Fujiwara Effect. Irwin may eventually be absorbed by Hillary southwest of the Cabo Peninsula over the weekend or early next week.
The second month of the 2017 Atlantic hurricane season winds down. On Saturday, dry African Saharan air keeps convection limited with a few tropical waves in the Atlantic and Caribbean. Saharan air outbreaks are very common in July. No tropical cyclone development is expected for at least the next 5 days.
As we shift to August and September all eyes are on the Main Development Region between the Caribbean and Africa. Water temperatures run 1-1.5 C above average. This could aid in a more active period as we approach the peak of the season (September 10th). Most computer models keep the Atlantic basin quiet for the next week. On average, the first hurricane in Atlantic forms on August 10th, therefore, it’s pretty common for July to wrap up on a quiet note.
Tropical Storm Don dissipated over the last 24 hours and it’s remnants are slowly moving through the southern Caribbean. With that system out of the way, we turn our eyes to a weak tropical wave (Invest 96L) in the Central Atlantic. As of Wednesday afternoon, the National Hurricane Center gives this only a 30% chance of development over the next few days as it moves west-northwest.
Like Don, high wind shear and dry air aloft will ultimately keep Invest 96L from developing into anything of consequence, but nonetheless we’ll keep an eye on it through the rest of the week.
It is still a bit early in the season for these Central Atlantic waves to develop into strong tropical systems, but as we head into the months of August and September, expect things to get more active. In fact, on average since 1950, 61% of named storms have formed over the next couple of months.
Don becomes the 4th named storm of the 2017 Atlantic hurricane season Monday. On average, the 4th named storm of the Atlantic season forms on August 23rd, so this is about one month ahead of schedule. Data from hurricane reconnaissance aircraft confirms a closed area of low pressure formed with winds up to 40 mph. Don is a tiny tropical storm. Winds only extend out 25 miles for the center. At 5 PM Don moves west at 17 mph. At this pace, tropical storm conditions will reach portions of the Windward Islands overnight Tuesday into Wednesday morning. A Tropical Storm Warning is in effect for Grenada. A Tropical Storm Watch is in effect for
Barbados, St. Vincent, the Grenadines, and St. Lucia. Only some strengthening is expected before landfall due to dry air in the mid levels of the atmosphere. Beyond landfall, Don will run into a wall of wind shear in the eastern Caribbean and dissipate mid-week.
Water vapor imagery shows a pocket of dry African air directly in the path of the newly named storm. This is indicated by the red color.
As mentioned above, dry air and increased wind shear should keep Don as a weak tropical storm. By Wednesday and Thursday it encounters strong westerly shear over the open Caribbean waters.
Behind Don is an area of disturbed weather between Africa and the Lesser Antilles. Convection is disorganized Monday due to a bit of dry air. There is a low 30% chance of tropical development the next 5 days as the tropical wave moves west-northwest. It will battle dry African air and increased moderate wind shear in the days ahead.
Former Tropical Depression Four hasn’t given up yet. Convection has flared up yet again Monday morning, as the disturbance pulls away from a nearby upper level low. As it does so, moderate wind shear will drop some in the days ahead. The tropical wave approaches south Florida mid to late work week and enhances daily sea breeze showers and storms. Hurricane Hunters are scheduled to investigate the area of disturbed weather Tuesday, if necessary.
The tropical wave southwest of the Cabo Verde Islands is worth keeping an eye on. While it is disorganized Monday and will battle dry African air over the next 5-7 days, some models still hint at tropical development. As of Monday morning the National Hurricane Center says there is a 20% chance a tropical depression/Tropical Storm Don forms over the next 5 days.
While the European model does not develop this feature, the GFS is consistent that a tropical storm may form as it nears the Lesser Antilles Friday and Saturday. The GFS is however extremely inconsistent on a long-range track. Each 6 hour run has varied greatly the past couple of days. At this point, model trends are worth watching for at least the next couple of days.
On Sunday, officially the National Hurricane Center expects no tropical cyclone development over the next 5 days. We are however, keeping an eye on a couple of features. The remnants of Tropical Depression Four is moving west-northwestward north of the Lesser Antilles. Convection has flared up some since the disturbance degenerated into a tropical wave Friday. Wind shear is elevated with an upper level TUTT low nearby, but wind shear will be dropping in the days ahead as the disturbance approaches the Bahamas and eventually Florida later this work week. It will encounter some dry air over the next couple of days.
The European model shows low wind shear Thursday and Friday near Florida, the Bahamas and the southwest Atlantic. The 0Z Euro tries to regenerate Tropical Depression Four over the warm Atlantic waters near the Carolinas early next work week.
A tropical wave that emerged off of Africa Saturday is worth watching. There is plenty of dry Saharan air in its path early this work week. The European model has backed off on tropical cyclone development the past few days. The GFS is back and forth, but is more insistent on development in recent model runs. The next named storm is Don.
The 06Z GFS develops Tropical Storm Don between the Lesser Antilles and Africa mid-work week. At this pace tropical storm conditions could reach the islands late Friday. Stay tuned.
In the east Pacific, Hurricane Eugene rapidly intensifies and becomes a major hurricane south of the Baja peninsula. It will steadily weaken over cooler waters this work week. It is no threat to land.
Invest 94L was still churning in the open Atlantic waters, about 850 miles WSW of the Cabo Verde islands at 2pm Wednesday EDT. The low pressure system developed a closed surface circulation Wednesday morning, as evident from satellite imagery and a Wednesday morning ASCAT pass. The system was also developing an increasing amount of thunderstorm activity, though mainly on the west side of the low. The chances for development of 94L into our next tropical depression was lowered to 60% Wednesday afternoon from the National Hurricane Center.
Part of the reason the chance of development has been lowered is because time is running out for 94L to become better organized. While conditions right now are marginally conducive to development, they become less favorable over the next couple of days. As the low moves farther west-northwest, it will run into an area of moderate to strong wind shear.
In addition, there is quite a bit of dry air on the north and west side of the system, thanks mainly to the Saharan Air Layer. That dry air is likely already impeding development, and will continue to do so in the coming days.
Either way, the low will continue on a west-northwest trajectory in the next 3-5 days, eventually sliding a few hundred miles north of the Lesser Antilles by this weekend. At that point, many of the models completely open up the wave and see no further development from it. The GFS keeps a very week system through that timeframe.
Meantime, Colorado State researchers have updated their latest hurricane forecasts. The upward trend in the numbers continues with this update – they now predict 15 named storms, 8 hurricanes, and 3 major hurricanes (including the 3 named storms we have already had). That trend has been primarily because of the increased likelihood of no El Niño this summer and an increase in Atlantic SST in the MDR (Main Development Region), although the latter has slowed down in recent weeks.
On Monday, Invest 94L is still disorganized. The broad area of low pressure is nearly stationary with scattered pockets of showers and storms. Wind shear is marginally favorable for gradual organization by Thursday and Friday. The disturbance is separated from the most of the intense dry, Saharan air nearby. The NHC ups the odds of tropical depression/Tropical Storm Don development to 70% over the next 5 days.
Computer models suggest a west-northwest path over the next 4 or 5 days. A few bring it close to the northeast Caribbean this weekend. As of Monday afternoon, most intensity models develop Tropical Storm Don by Wednesday or Thursday. It’s still too early to say if it stays out to sea as a stronger system or heads further west towards the Caribbean as a shallow/weaker one (and possible dissipate).
Dry air could hinder long-term organization and development. Water vapor imagery shows dry air east of the Lesser Antilles and north of the Caribbean.
Both the ECMWF and the GFS show Tropical Storm Don a few hundred miles east of the Lesser Antilles by late Thursday/early Friday. The Euro takes future Don further west and dissipates it southeast of the Bahamas by Monday. The GFS has been all over the place with track and intensity. The 12Z run suggests a recurve east of the U.S. through next work week. Stay tuned.
The second month of the 2017 Atlantic hurricane season begins Saturday. In July, we watch the Gulf Mexico, western Atlantic and the western and eastern Caribbean for tropical development. Climatologically, the first name storm of the season forms on July 9th. In 2017, two named storms, Bret and Cindy, formed in June. Arlene formed in April.
On Saturday, a weak tropical wave southwest of the Cape Verde Islands bears watching. It produces widely scattered, disorganized showers and storms as it moves westward at about 10-15 mph. While wind shear in the vicinity will stay pretty light the next few days, there is plenty of dry air in its path. Upper level winds increase as this the tropical wave approaches the Caribbean late next week. Nonetheless, gradual development is possible. As of Saturday morning, The NHC puts those odds at 20% over the next 5 days.
Water vapor imagery shows the weak tropical wave has dry, Saharan air in its path towards the Caribbean.
The 06Z GFS continues to hint that a weak tropical storm may form east of the Lesser Antilles by Thursday or Friday. The 0Z Euro also suggests a closed low may form by Thursday, but is a bit slower to approach the Caribbean. It’s something to keep an eye on the next few days. It’s way too early to talk about the long-term strength/path of this potential tropical system.
The last week of June winds down in the Atlantic Basin. From June 21-June 30th most named storms originate or develop in the Gulf of Mexico, western Caribbean or western Atlantic. 34 named storms have formed during this time period since 1851. The graphic below is courtesy Google Earth. As we transition to July, the common locations for tropical cyclone development shift a little further east.
Cape Verde season typically doesn’t peak until August and September. In rare fashion, another healthy tropical wave is set it emerge of Africa Thursday or Friday. As of Monday afternoon the NHC says there is a low 20% chance a tropical depression will form over the next 5 days.
There is plenty of dry Saharan air covering much of the central Atlantic and Caribbean. While this tropical wave will avoid some of the driest air in the coming days, it will run into a more hostile environment by the weekend. The graphic below is courtesy the NOAA/University of Wisconsin.
Dora became the first hurricane of the eastern Pacific season Monday. The tiny hurricane gradually weakens Tuesday as it runs into slightly cooler waters. It will pass well southwest of southwest Mexico, but rough surf is expected.