Teenager. Weather aficionado. Soccer fan. Realist. Posts subject to sarcasm. Goal: National Hurricane Center.
By: TropicalAnalystwx13 , 4:01 AM GMT on June 23, 2013
It has been a while since my last blog. In fact, during the duration, the Atlantic's second named storm – Barry – has developed and dissipated. Its origins trace back to a tropical wave that emerged off the coast of Africa in early June. Tracking westward, the wave remained disorganized until the western Caribbean. A piece of energy from the monsoon trough helped spawn a tropical disturbance that formed an area of low pressure on June 16. Radar data the following morning indicated the presence of a well-defined and closed center while satellite imagery depicted sufficiently organized convection for the National Hurricane Center to declare Tropical Depression Two. Little organization took place thereafter due to the system's proximity to the coast; Two made landfall near Monkey River Town a few hours later. Due to a passing trough across the central United States, falling heights caused the depression to jump erratically northward over the Yucatan, and it emerged into the Bay of Campeche on June 18 despite many forecasts of simply dissipating inland. Over warm sea surface temperatures and in an environment of only moderate wind shear, Tropical Depression Two steadily consolidated, likely due to the curvature of the Bay of Campeche which helps strength the anticyclonic flow of the low-pressure center. Deep convection blossomed atop it, and a Hurricane Hunters mission into the storm on June 19 indicated the presence of tropical storm-force winds; the NHC accordingly designated it Barry.
Following the departure of the aircraft, Barry continued to organize into the evening and overnight hours. Spiral banding began to develop and a central dense overcast was noted on satellite imagery. Satellite intensity estimates were very conflicting on the intensity on the cyclone. Estimates from SAB and TAFB revealed the organization of a tropical depression with T-numbers ranging from T1.0-T2.0, while intensity estimates from UW-CIMSS peaked just below 70 mph. In an effort to take into consideration both systems, and the fact that microwave loops prior to landfall indicated the formative stages of an eyewall open to the southwest due to the proximity to the coastline, I believe Barry peaked as a 50 mph tropical storm; it should be stated that stronger winds may have been found if a plane had investigated the storm right before landfall, due once again to the curvature of the Bay of Campeche. Officially, the National Hurricane Center states Barry peaked as a 45 mph cyclone, though I imagine this will be raised some in post-season analysis. Early on June 20, Barry made landfall as a minimal tropical storm; it weakened to a tropical depression a few hours later, and by late that day, the NHC determined Barry no longer had the convective structure of a tropical cyclone and declared it a post-tropical cyclone accordingly. The circulation gradually rained itself out over inland Mexico.
Figure 1. Infrared satellite imagery of Tropical Storm Barry at estimated peak intensity.
And now we are in the present, where tropical troubles have transitioned from the Atlantic to the eastern Pacific. This is where the National Hurricane Center has dubbed two invests – 94E and 95E – which both have good chances of becoming tropical cyclones in the near future. This sudden uptick in activity after a month of quiet can be attributed to an unusually intense pulse of the Madden-Julian Oscillation, a wave of enhanced precipitation and atmospheric lift that travels around the globe every 30 or so days.
Invest 94E is a very sprawling invest for the time being. In fact, it has the structure and appearance of a western Pacific, monsoonal-type disturbance. These types of storms typically take a while to consolidate, but often intensify quite rapidly once organized; this case will probably end up no different. Recent satellite images reveal the system is indeed pretty far from tropical cyclone designation at the current time, with a large mass of deep convection located mainly south of the broad and open – supported by southerly winds on the south side of the center as evidenced by a 16:25z ASCAT pass – area of low pressure. As of the latest ATCF update, 94E had maximum sustained winds of 30 mph with a minimum barometric pressure at 1006 millibars. The disturbance was moving west at 5 to 10 mph. The National Hurricane Center is currently giving the invest an 80% of developing into a tropical cyclone within 48 hours. I believe these chances are high and nearly certain, at ~100%. This system will likely become a tropical cyclone during the day tomorrow.
Figure 2. Infrared satellite imagery of Invest 94E.
Forecast for 94E
Invest 94E lies within a favorable environment for intensification, potentially quick. Wind shear images from the University of Wisconsin-Madison indicate an anticyclone atop the disturbance. Accordingly, the latest SHIPS file initialized with 8 knots of wind shear and forecasts shear generally less than 15 knots through the 120 hour period forecast. Sea surface temperatures are expected to remain favorable for intensification through 72 hours, when the disturbance is forecast to cross the 26°C isotherm. Relative humidity values are very high as a result of the MJO, with values into the mid- to upper 80s (%). Ocean Heat Content values lie at or above above 45 10^23 J through 48 hours before dropping off significantly. Despite the favorable parameters, the SHIPS only gives 94E a 4-in-10 chance of rapid intensification - an 25 knot increase in winds within 24 hours - for the entire period. This may be low. My forecast follows a majority of the statistical model guidance. Invest 94E is expected to be a tropical depression within 24 hours, a tropical storm within 36 hours, and a minimal hurricane shortly thereafter. Steady weakening is expected to begin in 72 hours due to decreasing sea surface temperatures.
The track forecast for Invest 94E is straightforward. The disturbance currently lies within an region of uniform steering, and is accordingly drifting westward to west-northwestward. This motion is expected to quickly shift north-northwestward as it feels the weakness between the area of high pressure over the northern Pacific and the temporarily weakening area of high pressure over central Mexico. By 72 hours, the ridge over Mexico is expected to build as the trough over the central United States lifts northeastward, forcing the storm on a more west-northwest trajectory. While 94E is not expected to make landfall as a tropical cyclone, or at all, its proximity to the coastline and what should be an intensifying tropical storm in 48 hours may produce dangerous rip currents and heightened surf along portions of the coastline of northern and central Mexico.
INIT 22/0000Z 30 KT 35 MPH
12H 23/1200Z 35 KT 40 MPH
24H 24/0000Z 40 KT 45 MPH
36H 24/1200Z 50 KT 60 MPH
48H 25/0000Z 55 KT 65 MPH
72H 26/0000Z 65 KT 75 MPH
96H 27/0000Z 55 KT 65 MPH
120H 28/0000Z 35 KT 40 MPH
Invest 95E may develop
As mentioned earlier in the blog, there is also another disturbance in the eastern Pacific. Dubbed Invest 95E, this system also has a chance for tropical cyclone formation over the next day or two. Visible satellite loops reveal a vigorous low-level circulation, and in fact, an ASCAT pass from all the back to early yesterday afternoon revealed a closed center of circulation. Shower and thunderstorm activity, the main reason this hasn't been classified yet, remains very disorganized and weak, and actually has been dissipating as of late. This may be attributed to diurnal changes; if so, we should expect an uptick in activity near sunrise. The National Hurricane Center is currently giving this area of disturbed weather a 30% chance of tropical cyclone formation; I give it an uncertain 60% chance of development due to the favorable conditions expected for the next day and a half to two days. If convection does not increase, this will not get designated.
Figure 3. Infrared satellite imagery of Invest 95E.
Forecast for 95E
The forecast for Invest 95E is so uncertain I question why I'm even writing this section at 11:08 pm...I have better things to do. I guess we'll start with intensity. The environment the invest is in right now isn't particularly unfavorable. Wind shear was analyzed at 9 knots by the SHIPS, light because 95E has an anticyclone like its sibling. Sea surface temperatures are near 28°C and relative humidity values are in the upper 60s (%). All three are expected to remain favorable over the next 36 hours, and perhaps become even more so as the disturbances drifts eastward...which we'll get into later...into higher into a region of higher atmospheric humidity. After 36 hours, wind shear is expected to skyrocket. This is due to Invest 94E, which should be a developing tropical storm at the time. Outflow from a system impacts strong wind shear on another, often dissipating the weaker storm. My uncertain forecast calls for 95E to attain tropical depression in 24 hours, though it may do it sooner or not at all, tropical storm status thereafter, and then depicts rapid weakening from there on out.
The track forecast is highly unusual; in fact, I've never had to forecast something like this before. The convectively-coupled Kelvin Wave and strong MJO pulse have spawned two tropical disturbances in close proximity to one another, and one or both are expected to become tropical cyclones. This brings in a rare phenomena called the Fuhiwhara, or binary interaction, effect. During binary interaction, two cyclonic vorticies orbit around one another. This effect is rare, and has only occurred a handful of times in the Atlantic and East Pacific combined. During the Fujiwhara effect, one of two things can happen: a) a smaller tropical storm interacts with another small tropical storm to form a larger and more potent tropical cyclone or b) a larger tropical storm interacts with a smaller tropical storm, in which case the larger tropical cyclones absorbs the weaker one. During the 1995 Atlantic hurricane season, Category 2 Hurricane Iris revolved around Category 2 Hurricane Humberto before absorbing a third tropical cyclone, Tropical Storm Karen. During the 2005 Pacific hurricane season, Category 1 Hurricane Max absorbed Tropical Storm Lidia. In this particular case, Invest 94E is expected to be the larger and stronger tropical cyclone. As far as 95E's track fate, 94E should pull the system towards it and gradually begin to absorb it. Nothing should be left of 95E after 72 hours.
INIT 23/0000Z 25 KT 30 MPH
12H 23/1200Z 30 KT 35 MPH
24H 24/0000Z 35 KT 40 MPH
36H 24/1200Z 35 KT 40 MPH
48H 25/0000Z 30 KT 35 MPH
72H 26/0000Z 20 KT 25 MPH...MERGING WITH 94E
Atlantic to turn active
The upward pulse of the Madden-Julian Oscillation doesn't typically stall in one basin forever. It will make its way from the East Pacific to the Atlantic at some point, likely during the first week of July. While most global models remain in agreement with the propagation of the wave, many differ in terms of intensity. The ECMWF and its ensembles are the least enthused about the intensity of the wave, while the GFS and its ensembles are the most bullish. The UKMET is a compromise of both models, but differs from both in terms of track. Overall, we should expect the MJO to move through Ocants 8, 1, and 2 – the western hemisphere – during early July.
The MJO is a very important player in early season development in the tropics, which does include the Atlantic. Accordingly, many global models have begun to depict tropical cyclone formation during the first few days of July in the western Caribbean, where the MJO pulse is expected to be most potent at the time. It should be noted that many models are often too progressive with development and that we should watch for them to push back the development time frame a few days as it adjusts. The GFS did something similar the past few days, showing a tropical cyclone in the Gulf of Honduras in 8 days from a tropical wave in the eastern Atlantic. Previous runs showed it moving northward into the eastern Gulf Coast by day 10; however, recent runs of the GFS have pushed back development. With pressures low, high pressure building north over the East United States – therefore forcing convergence south into the western Caribbean and Gulf of Mexico – and the idea that many model ensembles show development by the ends of their runs, this area should be watched the first and second week of July for development. This MJO pulse may be responsible for 3 or so tropical cyclones and a hurricane or two as it persists in the Atlantic through the first half of July. We have a relatively decent chance of seeing our first Cape Verde storm...or at least central Atlantic storm...during this time as well.
Figure 4. Recent models' depiction of the MJO pulse.
One area of interest over the following days is expected to be a strong tropical wave currently in the Intertropical Convgergence Zone near 40W. This wave has shown signs of organization over the past day, and conditions are expected to be generally favorable for further development as it tracks west-northwest at 15 to 20 mph. Sea surface temperatures are above 26°C, anticyclonic flow is noted aloft, and precipitable water loops reveal a deep moisture bubble with the wave which should protect it from dry air nearby. While none of the models develop it, understandably, the GFS does briefly show tropical storm-force winds in association with the wave in two to there days. While I only give this a 10% chance of becoming a tropical cyclone in the short term, this may be the feature many models have been hinting at for development in the western Caribbean in the long run, so it should be watched.
A small area of low pressure developed along the tail-end of a dying cold front last night and early this morning. Despite wind shear and high surrounding atmospheric pressures, the low managed to become quite well-defined; surface observations as it made landfall on the southeast North Carolina coastline revealed a broadly closed center. The National Hurricane Center briefly mentioned it in their Tropical Weather Outlook this morning and designated it an invest, but development was not expected. Had this system remained over water for another day or so, it likely would have become a tropical cyclone. This is just a remainder of how quickly systems can spin up.
I will have a new blog tomorrow afternoon,
Comments will take a few seconds to appear.