TropicalAnalystwx13's WunderBlog

Tropical Depression Four-E likely to affect the coastline of Mexico as a hurricane

By: TropicalAnalystwx13, 3:57 AM GMT on June 30, 2013

The fourth tropical cyclone of the 2013 Pacific hurricane season is here. After struggling to develop convection – shower and thunderstorm activity – much of last night and today, a sharp increase in coverage and intensity this evening allowed the National Hurricane Center to initiate advisories on Tropical Depression-Four E. As of the first advisory, Four-E was located within 30 nautical miles of 13.7N 103.0W, or roughly 305 miles southwest of Acapulco, Mexico. Maximum sustained winds were up to 35 mph, and the minimum barometric pressure was down to 1006 millibars. The system was moving towards the north at 10 mph. Latest satellite intensity estimates from UW-CIMSS and SAB were both T2.0/35 knots; SSD Dvorak has yet to be initiated. Satellite loops reveal Four-E is a well-organized system, with bursting deep convection over the low-level circulation and great outflow mainly in the western semicircle. In addition, a microwave pass from a few hours ago revealed a prominent curved band extending south of the circulation. A secondary band appears to be developing north of the circulation. Needless to say, given the environment, Four-E is expected to become a tropical storm very shortly.



Forecast for Four-E
The environment ahead of the tropical depression is quite favorable for intensification. Shear maps from the University of Wisconsin-Madison indicate the presence of an anticyclone in the upper levels of the atmosphere. This feature should act to keep wind shear on the tropical cyclone low over the next few days; in fact, the SHIPS indicates shear generally lower than 10 knots throughout the entire forecast period. Sea surface temperatures were analyzed at nearly 30°C; these values are more than favorable for development, and will likely remain so for another 72-96 hours. After that time, the system is expected to lose the warm ocean heat source as it gains latitude. Relative humidity values between 700-500mb are currently in the mid-70s (%) and should generally remain ±10% throughout the entire period. Ocean heat content is forecast to drop to 0 between 72-96 hours. Despite these seemingly favorable conditions, a majority of the statistical and global model guidance keeps Four-E below hurricane intensity. At the expense of totally blowing this forecast, I maintain my intensity forecast from yesterday evening in showing steady intensification over the next 24 hours followed by more rapid intensification after an inner core is well-built. Four-E is expected to peak as a 100 mph Category 2 hurricane in 72 hours; my forecast is a full 30 mph above the National Hurricane Center's, which in return is well above the aforementioned guidance.

Despite the disagreement in the intensity forecast for Four-E, the statistical and global model guidance remains in remarkably well agreement for the track of the system. Four-E is currently being steered nearly due north in response to a weakness provided by an elongated upper-level low from the Gulf of Mexico to the northwest of the depression. This general motion is expected to continue over the next few hours. Thereafter, the beast of a ridge of high pressure positioned over the Four Corners region is expected to become the dominant steering mechanism. This should result in Four-E bending towards the north-northwest, northwest, west-northwest, and eventually west by 120 hours as it becomes an increasingly shallower system. Until then, however, there is a good chance the tropical depression brings effects to the coastline of Mexico. On its current project path, Four-E would pass less than 200 miles from land, meaning outer bands capable of producing tropical storm-force winds in excess of 40 mph and torrential rainfall of 1-3 inches are likely in the region. As a result, the Government of Mexico has issued a Tropical Storm Warning from Punta San Telmo to Manzanillo, Mexico, and a Tropical Storm Watch from north of Manzanillo to La Fortuna, Mexico. A warning means tropical storm conditions are expected within 36 hours, while a watch means such conditions are possible within 36 hours.

...FORECAST POSITIONS/MAX WINDS...

INIT 30/0300Z 13.7N 103.0W 30 KT 35 MPH
12H 30/1200Z 14.8N 103.1W 35 KT 40 MPH
24H 01/0000Z 16.0N 103.9W 40 KT 45 MPH
36H 01/1200Z 17.2N 104.6W 55 KT 65 MPH
48H 02/0000Z 18.0N 105.2W 75 KT 85 MPH
72H 03/0000Z 19.1N 106.9W 85 KT 100 MPH
96H 04/0000Z 19.6N 108.6W 70 KT 80 MPH
120H 05/0000Z 19.6N 111.1W 55 KT 65 MPH

I will have a new blog on Four-E in the morning,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

Updated: 4:00 AM GMT on June 30, 2013

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Invest 96E likely to affect Mexico; potent tropical wave east of the Lesser Antilles

By: TropicalAnalystwx13, 3:37 AM GMT on June 29, 2013

It's only been three days since my last blog, but since that time we've the East Pacific has birth another disturbance well on its way to becoming a tropical depression. Dubbed Invest 96E, the National Hurricane Center is currently giving the disturbance an 80% chance of tropical cyclone formation within 48 hours. Satellite loops reveal the system is well organized, with a defined and presumably closed low-level circulation and prominent outflow pattern. Shower and thunderstorm activity has been on the decrease over the past few hours, but this may just be a result of diurnal minimum - when the instability between the land and ocean is at its lowest. The latest satellite intensity estimates from SAB were T1.5/25 knots; in order for advisories to be initiated on a tropical cyclone, a value of T2.0/30 knots is typically needed. It is likely that 96E will attain tropical depression status tomorrow morning, and I give it a Near 100% chance of becoming a tropical cyclone over the next 48 hours accordingly.


Figure 1. Black/white infrared satellite imagery of Invest 96E.

Forecast for 96E
Invest 96E is in a very favorable environment for intensification. Maps from the University of Wisconsin-Madison indicate the presence of anticyclonic flow in the upper 200 millibars of the atmosphere. This is providing low wind shear for the tropical disturbance, and these favorable values of less than 10 knots are forecast by the SHIPS to remain throughout the entire period. Sea surface temperatures are currently around 29C, and may increase ever so slightly before becoming unfavorable for further development at the end of the forecast period. Relative humidity values between 700-500mb were analyzed in the lower 80s (%) but are expected to perhaps be the most detrimental to development; values should drop into the upper 60s to lower 70s after 48 hours. Heat content is currently in the 20s (kJ/cm^2) but is forecast to increase to the 50s by 48 hours. Unlike Cosme, Invest 96E is a very compact system; this greatly increases its chances of rapid intensification under favorable atmospheric conditions. In fact, the SHIPS is giving the disturbance a 6/10 of 25-kt rapid intensification over the next 2 days. All things considered, I expect 96E to become a tropical depression in the morning and a tropical storm tomorrow afternoon. Steady intensification should occur thereafter, at least until a well-defined inner core is built. I expect Invest 96E to attain hurricane intensity in 48 hours, and peak as a low-end Category 2 in 72 hours. Decreasing sea surface temperatures will likely slowly weaken the storm at the end of the period.

Models remain in impressive agreement regarding the forecast track of Invest 96E. Though the storm has been tracking generally west, an abrupt shift to north or north-northeast is expected over the next 24 hours as a result of troughiness over inland Mexico and the Gulf of Mexico. This motion is expected to continue for roughly 48 hours; after this time, an expanding region of high pressure is expected to replace the troughing over Mexico and force the storm northwest and likely west-northwest towards the end of the period. It should be stated that the current model guidance shows the center of what should be a potent hurricane at the time passing less than 200 miles from the coastline of Mexico. Any small change in the pattern north of the storm may lead to huge changes in the track. Regardless of a landfall, outer bands are likely to impact the coastline from Mazatlán to Acapulco. These bands are likely to deliver gusty winds, possibly in excess of tropical storm-force, and torrential rainfall capable of producing mudslides, landslides, and street flooding. Wave heights along the coastline are expected to be abnormally high, and rip currents will become a great concern for beach-goers. Tropical cyclone advisories will likely be needed for a stretch of the coastline of Mexico accordingly.

...FORECAST POSITIONS/MAX WINDS...

INIT 29/0300Z 10.8N 104.6W 25 KT 30 MPH
12H 29/1200Z 11.7N 104.2W 30 KT 35 MPH
24H 30/0000Z 13.1N 103.9W 40 KT 45 MPH
36H 30/1200Z 14.6N 103.9W 50 KT 60 MPH
48H 01/0000Z 16.2N 104.4W 65 KT 75 MPH
72H 02/0000Z 18.2N 106.2W 85 KT 100 MPH
96H 03/0000Z 19.1N 108.3W 80 KT 90 MPH
120H 04/0000Z 19.0N 109.9W 75 KT 85 MPH

Tropical wave near Lesser Antilles
An impressive tropical wave for this time of the year - something we've seen countless times so far this season - is currently located near the Lesser Antilles. Satellite loops reveal the tropical wave is disorganized, with meager convection located mainly in the eastern semicircle of the wave axis. However, surface observations and data from global model guidance wind maps indicate that the wave actually has a well-defined and closed low-level circulation. The National Hurricane Center is currently giving this wave a Near 0% chance of development within 48 hours; I agree with these chances. While the wave is abnormal for this time of the year, and likely a sign of things to come next month and on, high wind shear from the subtropical jet stream is expected to deter any tropical development, at least until the southwest or west Caribbean. Once it reaches this region, lower wind shear and the influence of the upward pulse of the Madden-Julian Oscillation and a convectively-coupled Kelvin Wave may spark development, as indicated by the GFS ensembles. Regardless of any development, this wave is likely to bring heavy rainfall and gusty winds to the islands occupying the southern Caribbean Sea.


Figure 2. Black/white infrared satellite imagery of the tropical wave located east of the Lesser Antilles.

Cosme of little concern
I apologize for the lack of blogs on Cosme over the past few days. Since my previous one, Cosme peaked in intensity as a strong Category 1 hurricane, and ultimately died a typical death across the East Pacific; a result of cooler sea surface temperatures and stable air aloft. The circulation remains very well-defined on satellite imagery, and is undoubtedly closed. However, due to the factors that killed it, the remnants of Cosme are not expected to be a candidate for redevelopment. The low-level circulation is likely to continue tracking due west and may impact the Hawaiian islands in a little under a week. Due to the orography of the islands, locally torrential rainfall may result. Higher waves and an increased threat of rip currents may accompany the system as well; overall, there is little need for concern.

I'll have a new blog on what should be the next East Pacific tropical depression tomorrow,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

Updated: 3:53 AM GMT on June 29, 2013

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Hurricane Cosme nearing peak intensity; Caribbean development and thoughts on season

By: TropicalAnalystwx13, 4:06 AM GMT on June 26, 2013

Cosme is continuing on its west-northwest journey tonight and is gradually intensifying while doing so. As of the latest National Hurricane Center advisory, the system was located within 15 nautical miles of 17.9°N 113.3°W, or about 410 miles south-southwest of Cabo Corrientes, Mexico. Maximum sustained winds were up to 85 mph, making Cosme a Category 1 on the Saffir-Simpson hurricane wind scale, and the minimum barometric pressure had fallen to 981 millibars. The cyclone was moving towards the west-northwest at 14 mph. Despite the increase in winds from the previous advisory, Cosme is likely very near or past its peak intensity. While a microwave pass from just a few hours ago indicates the system is maintaining a closed eyewall, the banding eye feature observed on visible satellite loops earlier has began to fade in recent frames. In addition, convection is weakening and taking on a more ragged appearance. Satellite intensity estimates were T4.0/65 knots and T4.5/77 knots from SAB and TAFB, respectively, while estimates from UW-CIMSS and SSD Dvorak were T4.6/80 knots and T4.1/67 knots, respectively. Cosme is a very broad hurricane, with hurricane-force winds extending out 35 miles from the center, and tropical storm-force winds extending out 175 miles from the center.


Figure 1. Visible satellte imagery of Hurricane Cosme. At the time, the cyclone contained maximum sustained winds of 80 mph.

Forecast for Cosme
The upper-level outflow pattern associated with Hurricane Cosme has greatly expanded over the past 24 hours; this is indicative of a much improved upper-air shear pattern. Similar to past days, 700-500mb relative humidity values remain among the highest ever observed for a tropical cyclone in this part of the world, with values exceeding 80%. These seemingly favorable conditions for intensification over the following days will be offset by a steep drop in ocean heat content and surface temperatures. The latest SHIPS file analyzed the storm over 26.2°C waters, and these values are only expected to decrease over the coming days as Cosme moves west-northwest. Several statistical models show a rapid decrease in intensity over the next 48 hours, with Cosme losing hurricane intensity within 36 and tropical cyclone status by as soon as 72 hours; the NHC forecast does not differ. Due to the storm's large size, I feel such quick weakening is probably a little too quick. I expect Cosme to lose hurricane intensity late tomorrow afternoon and tropical storm status early Wednesday morning. Cosme is expected to degenerate into a tropical cyclone Friday evening, if not a little sooner.

The track forecast for Cosme is essentially unchanged from several days ago. The cyclone is on a 290/12 heading, steered west-northwest due to a mid-level ridge over north-central Mexico. This motion is expected to continue for as long as the system remains a tropical cyclone. After 96 hours, the remnant circulation associated with Cosme is expected to become embedded within the west-east flow across the Pacific Ocean. My forecast slightly farther north than yesterday's update and in direct agreement with the statistical model consensus. While Cosme is not expected to make a direct landfall on any stretch of the coastline of Mexico, the storm's broad size has been delivering heavy squalls to the coastline, producing locally heavy rainfall. In addition, its large region of gale-force winds has resulted in increased rip currents and wave heights along the coastline. These waves and currents are expected to parallel the system, and should affect Baja California Sur over the next few days before steadily subsiding.

INIT 26/0300Z 17.9N 113.3W 75 KT 85 MPH
12H 26/1200Z 18.6N 115.2W 70 KT 80 MPH
24H 27/0000Z 19.5N 117.6W 60 KT 70 MPH
36H 27/1200Z 20.3N 120.3W 50 KT 60 MPH
48H 28/0000Z 20.9N 123.1W 35 KT 40 MPH
72H 29/0000Z 22.0N 128.1W 25 KT 30 MPH
96H 30/0000Z 22.1N 132.8W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 01/0000Z 22.2N 136.8W 15 KT 20 MPH...POST-TROP/REMNT LOW

Watching the Caribbean
The development of Hurricane Cosme can be attributed, at least in part, to the Madden-Julian Oscillation, or MJO. The MJO is a wave of precipitation anomalies and air motions that contains two phases: the upward, or wet, pulse, and the downward, or dry, pulse. During the former, westerly winds on the leading edge of the wave collide with typical easterly winds to the east, creating surface convergence and lift and allowing thunderstorms to develop. During the downward phase, general subsidence - sinking air - deters the development of shower and thunderstorm activity, and typically contributes to drier than average weather. This wave is currently in the East Pacific, and may be the start of a busy time in the Atlantic starting late this week into next week.

A potent tropical wave is currently located over the Lesser Antilles. The CMC model has been consistent on this wave tracking west across the central Caribbean Sea and into the western portion of the region, where it interacts with a piece of energy from the monsoon trough - drawn north by a strong upper-level trough over the eastern United States - to begin tropical cyclogenesis east of Nicaragua. This same trough creates a weakness northwest of the disturbance while simultaneously eroding the western periphery of the unusually strong subtropical ridge, allowing for a general northward track. With the presence of an anticyclone while positioned over warm waters, the model gradually intensifies it, making it a good-sized hurricane in the Gulf become slamming ashore the Florida Panhandle the day before July 4th. While the exact track has been uncertain - one run showed Texas, the other Mississippi, and now Florida - the CMC has been consistent on both intensity and the idea of having a tropical cyclone to begin with.

The genesis of the disturbance is very similar on the GFS as it is on the CMC. The southern portion of the tropical wave over the Antilles tracks westward, interacting with the monsoon trough while located east of Nicaragua. Unlike the CMC, however, the GFS questionably - I say questionably because the model has a stronger trough than even the CMC does - tracks the storm into central America before any substantial development can begin. The model sends the remnant vorticity in the Bay of Campeche a few days later, where it becomes what should be a tropical cyclone and tracks generally northward into southwest Texas.

It is too early to be focusing on details. However, what should be taken away from both of these models is that the West Caribbean or Bay of Campeche will need to be watched for potential development as we head into late this week and into next week. The CMC is likely too aggressive with its forecast of an organized tropical cyclone while still in the northwestern Caribbean Sea, while the GFS is likely unrealistic with a track buried deep into Central America. Its forecast for little development may also be skewed due to the fact that it keeps the MJO pulse largely in the East Pacific; several ensemble members develop a tropical cyclone here instead. I do think there is a good chance we see a named storm out of this pattern, and this pattern does favor a track generally north towards the Gulf Coast of the United States. It should be watched. Development is never a guarantee.


Figure 2. The 12z CMC sends a Category 1 hurricane into the Florida Panhandle on July 3.

Continued thoughts on the hurricane season
It's been a few weeks since I last released my forecast for the 2013 Atlantic hurricane season. However, there have not been very many changes. The Pacific Decadal Oscillation remains negative, or in a negative-like pattern. The ENSO remains cool Neutral, though this may change as I will discuss a little below. In the Atlantic, sea surface temperature anomalies have come down over the past few weeks due to the usually strong Bermuda high. A stronger-than-average ridge promotes stronger-than-average trade winds across the Tropical Atlantic; stronger-than-average winds lead to more mixing of the skin temperatures than usual, leading to a slight decrease in values. However, the main thing to take away from now is that water temperatures remain higher relative to the world. When this occurs, the MJO has a tendency to become "stuck" in that particular basin and create a favorable setup for tropical cyclones. The Atlantic tripole remains evident, though shifted farther south than a few months ago, and is actually forecast to become more prominent as we head into July.

Since my last forecast, the Gulf of Guinea has cooled. A cool Gulf enhances the African Easterly Jet while shifting it slightly farther north than usual, leading to more robust tropical waves that have a greater potential to develop into tropical cyclone. And not surprisingly, many have noted the very potential tropical waves across the central Atlantic so far this season. Despite this, vertical instability continues to struggle in the central and eastern Atlantic as it has for the past few years. I should note that it briefly reached normal to above-normal values in late May. The recent decrease is likely due to the strength of the Bermuda ridge that has shunted the Intertropical Convergence Zone farther south than usual, limiting precipitation across the region. In addition, we have been in the downward pulse of the MJO for a few weeks. I suspect that as we head into next month it will make a bit of recovery.

There have been a few changes in the model forecasts for this season, with a trend generally towards a less favorable Atlantic. Earlier this month, the CFS switched from Neutral ENSO conditions to a full-blown El Nino by next month, with cooler-than-average sea surface temperatures and large regions of higher sea level pressures. The UKMET depicted high sea level pressures in the absence of an El Nino. Meanwhile, the ECMWF remains the least enthused of them all, with a moderate El Nino and very high pressures across the Atlantic. Over the few weeks, the CFS has began trending back towards a favorable pattern with much lower pressures stretching from Africa to the United States. I'm not sure where it's and the ECMWF's idea of an El Nino came from, and one in July at that, but it should have been and should be discounted. While equatorial Pacific sea surface temperatures are likely to warm quite a bit over the next two weeks as westerlies plague the region (little upwelling), the Southern Oscillation Inded (SOI) nor the El Nino Southern Precipitation Index (ESPI) are indicative of a long-lasting and significant warming event.

Overall, my forecast is unchanged. My forecast from early May called for 18 to 21 named storms, 8 to 12 hurricanes, and 3 to 5 major hurricanes, with an Accumulated Cyclone Energy index in excess of 150 units. It should be stated that my named storm forecast hinges on a few frontal/subtropical cyclones in the subtropics; if the Bermuda high remains as potent as it is now, we may not have an opportunity to see as many as in recent years, and my forecast may be a little generous. I still expect about 4 hurricane landfalls on U.S. soil, 1-2 of which may be Category 3 or above at landfall. Persistent ridging over Canada, an stronger than normal Bermuda high, and eastward-located high southeast of Alaska do not bode well for the coastline. This is a year where anybody could be impacted, and it's crucial to know what to do if a storm threatens your home. It only takes one.

I'll have a new blog on Cosme Thursday,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

Updated: 3:16 AM GMT on June 27, 2013

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Tropical Storm Cosme approaching hurricane intensity but poses no serious threat

By: TropicalAnalystwx13, 3:11 AM GMT on June 25, 2013

Tropical Storm Cosme is well on its way to hurricane intensity this evening following classification early this morning. As of the latest advisory from the National Hurricane Center, Cosme was located within 30 nautical miles of 15.9°N 107.9°W, or about 320 miles southwest of Manzanillo, Mexico. Maximum sustained winds were up to 65 mph and the minimum barometric pressure had fallen to 994 millibars. The system was tracking northwest at 14 mph. Recent satellite loops reveal a well-organized tropical cyclone, with deep convection over the center and south of it in a spiral band that extends well out from the storm. Recent microwave imagery shows a developing inner core with Cosme, depicting a banding feature and likely eyewall wrapping three-quarters around the center of circulation. Satellite intensity estimates from UW-CIMSS-ADT and SAB have remained nearly steady near T3.6/57 knots and T3.0/45 knots, respectively, but estimates from SSD-ADT have risen to T4.0/65 knots. Cosme is approaching hurricane intensity and is forecast to reach it early tomorrow morning.


Figure 1. Visible satellite imagery of an intensifying Tropical Storm Cosme at 20:15z.

Forecast for Cosme
Tropical Storm Cosme, after intensifying slower than forecast two days ago, has strengthened quite a bit more than I originally forecast today. Shear seems to have abated some based on satellite trends today, and indeed, the latest SHIPS file analyzed 4 knots of shear atop the cyclone. Cosme remains situated above sea surface temperatures in excess of 29°C and within a moist environment with 700-500mb Relative Humidity values at or above 87%. These conditions are sufficiently favorable for steady if not quick intensification, but Cosme's large size may deter rapid deepening. Considering trends today, I have raised my forecast from yesterday and now predict the cyclone to peak as a strong Category 1 in 24 hours or so. After this time, the storm is expected to cross the 26°C isotherm, enter a region of more stable air, and be deprived of any ocean heat content from below. Accordingly, Cosme is expected to lose hurricane intensity in roughly 48 hours and continue to rapidly weaken thereafter. A majority of the model guidance indicates the storm will weaken to a tropical depression in 84 hours or less; however, due to my forecast being slightly higher than a majority of the guidance, I am expecting the storm to lose that status a little later than indicated. Cosme is expected to become a remnant low at the end of the forecast period.

Tropical Storm Cosme continued to move towards the northwest, paralleling the coastline of Mexico, in response to a weakness to the storm's northwest. A mid-level ridge of high pressure is expected to intensify over the subsequent 24 hours; this should induce a gradual west-northwest bend in Cosme's track while steadily accelerating it. By days three and four, a due west and perhaps west-southwest bend is expected as the rapidly decreasing [in intensity] tropical cyclone becomes embedded within the swift east-to-west flow across the Pacific Ocean. My forecast track is a little quicker than yesterday and remains ever so slightly north of the latest National Hurricane Center track forecast. It is in agreement with a majority of the statistical and dynamical models. While Cosme is not expected to make a direct landfall on any landmass, its large size – with the circulation radius extending out over 300 miles and tropical storm-force winds extending out 175 miles – may produce locally heavy rainfall from Mazatlan to Ixtapa. Constant gale-force winds are expected to produce higher-than-average wave heights along the coastline, and there is a high risk for life-threatening rip currents.

...FORECAST...

INIT 25/0300Z 15.9N 107.9W 55 KT 65 MPH
12H 25/1200Z 16.8N 109.9W 65 KT 75 MPH
24H 26/0000Z 17.7N 112.3W 75 KT 85 MPH
36H 26/1200Z 18.2N 114.6W 65 KT 75 MPH
48H 27/0000Z 18.9N 117.0W 55 KT 65 MPH
72H 28/0000Z 20.2N 122.2W 40 KT 45 MPH
96H 29/0000Z 20.5N 127.1W 30 KT 35 MPH
120H 30/0000Z 20.4N 132.1W 25 KT 30 MPH...POST-TROP/REMNT LOW

Elsewhere, no tropical cyclone development is expected in the East Pacific over the next two days. I will have a blog on Cosme, my thoughts for the Atlantic hurricane season, and potential July development tomorrow,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

Updated: 6:05 PM GMT on June 25, 2013

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Tropical Depression Three-E forms, expected to become a hurricane

By: TropicalAnalystwx13, 3:14 AM GMT on June 24, 2013

The broad area of low pressure well south of the coastline of Mexico finally acquired enough organization this morning to be considered a tropical cyclone. As of the latest National Hurricane Center advisory, the system was located within 50 nautical miles of 12.6N 104.4W. It had sustained winds of 35 mph and a minimum barometric pressure of 1005 millibars. Three-E was moving towards the northwest at 7 mph after being nearly stationary all day. Visible satellite loops reveal the cyclone is still very much in its formative stages, with generally disorganized shower and thunderstorm activity located south of the broad low-level circulation. However, other than moderate wind shear of 10-15 knots, atmospheric conditions are favorable for steady intensification. The NHC predicts Three-E will intensify into a tropical storm over the next 12 hours, and further to a Category 1 hurricane by 48 hours. Overall, the main impediment for more substantial strengthening is the depression's very large size. The winds in a broad storm typically are forced to cover a larger area and usually take a longer amount of time to intensify.


Figure 1. Tropical Depression Three-E at the time of classification.

Forecast for Three-E
As aforementioned, the depression is situated within a favorable environment for continued development. Maps courtesy of the University of Wisconsin-Madison indicate an anticyclone in the upper 250 millibars of the atmosphere, though it is displaced slightly to the northwest. This is imparting moderate...not detrimental...northerly wind shear on Three-E. Sea surface temperatures lie above 29°C, and 700-500mb relative humidity values are in the upper 80s (%). Ocean heat content values are at or above 50 kJ/cm^2. These conditions are favorable for rapid intensification if the storm develops a well-defined inner core, and in fact, the SHIPS is giving the storm a slightly greater than 5-in-10 chance of undergoing a 30 mph increase in winds over the next 24 hours. The broad nature of Three-E may deter this, however. A majority of the statistical model guidance do not show intensification into a hurricane; however, based on the forecast from the DSHIPS and several global models, my own forecast is unchanged from yesterday in showing a peak intensity equivalent to a Category 1 hurricane in 48 hours. After that time, the storm is expected to enter a region of cooler sea surface temperatures and more stable air, inducing steady weakening. The storm may degenerate at the end of the period.

After remaining stationary for nearly 18 hours, the depression has begun to move northwestward in response to a weakness to the cyclone's northwest. This general northwest motion is expected to continue for the next day or so. Beyond that time, a now-weak area of high pressure across north-central Mexico is expected to build in intensity and force the storm on a more west-northwest trajectory while gradually accelerating. By 96 hours, the weakening storm is expected to turn due west as it becomes embedded within the east-west low-level flow. All statistical, dynamical, and global models remain in agreement for this solution. While Three-E is not expected to make landfall, outer bands may impact the coastline and produce locally heavy rainfall and gusty winds. Increased wave heights are expected, and there is a heightened risk of rip currents.

...FORECAST...

INIT 24/0300Z 12.6N 104.4W 30 KT 35 MPH
12H 24/1200Z 13.5N 105.0W 35 KT 40 MPH
24H 25/0000Z 15.1N 106.8W 45 KT 50 MPH
36H 25/1200Z 16.2N 108.9W 55 KT 65 MPH
48H 26/0000Z 17.2N 111.3W 70 KT 80 MPH
72H 27/0000Z 18.5N 116.2W 55 KT 65 MPH
96H 28/0000Z 19.4N 121.2W 40 KT 45 MPH
120H 29/0000Z 19.7N 126.3W 30 KT 35 MPH

Invest 95E no concern
After nearly becoming a tropical cyclone last evening, Invest 95E has faltered and is no longer a threat to develop. The well-defined low-level circulation has fallen apart into a weak area of cyclonic turning, and the little convection the storm possessed is being blown away by easterly wind shear produced by Three-E's outflow. Wind shear is expected to increase to over 40 knots by this time tomorrow, and the remnants and energy of the storm should begin to be absorbed into the depression farther east before then. The National Hurricane Center is currently giving this area a 10% chance of developing into a tropical cyclone over the next 48 hours; I put these odds lower, at Near 0%.

I will have a new blog on Three-E tomorrow evening,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

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Invests 94E and 95E likely to become cyclones; Atlantic may get active in July

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.

...MAX WINDS...

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.

...MAX WINDS...

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
96H...ABSORBED
120H...ABSORBED

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.

Elsewhere
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,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

Updated: 4:06 AM GMT on June 23, 2013

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Andrea becomes post-tropical, flooding rains continue; more development in June?

By: TropicalAnalystwx13, 3:13 AM GMT on June 07, 2013

Tropical Storm Andrea is no longer with us this evening. After making landfall on the Florida Big Bend yesterday evening with winds of 65 mph, Andrea began to accelerate and quickly lose its tropical characteristics as it felt the effects of the approaching upper-level trough to its west. The low-level circulation remained well-defined up until earlier afternoon, when it began to become elongated and less robust. In addition, surface observations across North Carolina and Virginia earlier this afternoon revealed the cyclone was becoming embedded with a stationary front; accordingly, the National Hurricane Center designated Andrea as a post-tropical cyclone in their 5pm EDT advisory. Typically, this would be the final bulletin on the storm; however, due to the controversy centered around Superstorm Sandy in October of last year, the organization enacted a new policy that allows them to a) continue to advisories on any tropical cyclone that has since transitioned into a post-tropical or extratropical cyclone assuming it poses a significant threat to life and/or property and b) allow tropical cyclone watches and warnings to remain in effect across the affected regions. As of the latest advisory from the National Hurricane Center, Andrea contained maximum sustained winds of 45 mph. The minimum barometric pressure had risen to 997 millibars, and the cyclone was racing towards the northeast at 35 mph. Infrared satellite imagery reveals Andrea has the classic appearance of a post-tropical cyclone, with transient convection north of the center and comma-shaped well removed otherwise.

Thus far, Andrea has produced weather not atypical for a mid-grade tropical storm. Winds along the coast of North Carolina topped out at 53 mph earlier this morning, and widespread 4-5" rainfall totals were observed. Several brief tornadoes, and waterspouts that moved onshore to become tornadoes, were observed as well. The tail-end of the post-tropical cyclone led to torrential rains across the metro area of Miami, where totals in excess of a foot were recorded. Hundreds of cars were stranded, and their residents had to be rescued. One death has been attributed to Andrea so far, linked to a traffic wreck...presumably due to the storm's bad weather across the region...in Virginia.


Figure 1. Infrared satellite imagery of Post-Tropical Cyclone Andrea.

Forecast for Andrea
Andrea has already completed the tropical phase of its life, and it is destined to complete the second phase of its lifespan shortly as well. A majority of the global models indicate that the remnants of Andrea should begin to turn more easterly as they become involved with the upper-level westerlies. After passing southeast of Newfoundland on Sunday, it is likely to be absorbed within a larger extratropical low across the northern Atlantic. In the meantime, however, potentially significant impacts are likely to occur across the Northeast. Several areas have already picked up several inches of rainfall, and a few more may occur before the cyclone moves on tomorrow evening. These rain totals will be capable of leading to isolated road flooding and overflowed river banks, both of which may threaten travel and property. Conditions are no longer favorable for the development of tornadoes, but a strong low-topped storm may be capable of producing a damaging wind gust or two. Localized coastal flooding is possible in conjunction with high tide along the New England shores. Winds of near-gale intensity are expected to impact Atlantic Canada late tomorrow through early Sunday.

Late June development
The 2013 Atlantic hurricane season has already featured one named storm, and now it's time to look down the road for potential development in late June. The CMC continues to indicate the development of a small tropical cyclone just off the eastern coast of Florida in 10 days or so; in fact, both the GFS and ECMWF have now followed suit in showing at least a weak area of low pressure. It should be stated that trough splits often result in small-sized tropical cyclones which are not resolved very well given the aforementioned model's resolutions. In addition to the trough split, the GFS has been very consistent in showing a tropical cyclone...originating from the monsoon trough that is effectively drawn north by the same trough that spawns the cyclone off the Southeast coastline...developing in the western Caribbean only a few days thereafter. Just FYI, the 18z GFS sends a minimal sub-985 millibar hurricane into the coastline of Mexico towards the end of its run. While the track and intensity is not to be worried about at this time, what we should start monitoring is the GFS ensemble mean. A handful of GFS ensembles currently develop this cyclone despite a lack of support from other global models; the GFS is usually best at detecting long range development. Even though the MJO is leaving our region of the world, tropical cyclones can and do form within the downward pulse of the MJO, and the tropics will have to be watched for mischief, especially after June 15.

I'll have a new blog early next week,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

Updated: 3:44 AM GMT on June 08, 2013

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Tropical Storm Andrea moves ashore; Invest 92L and the outlook for the rest of June

By: TropicalAnalystwx13, 3:12 AM GMT on June 07, 2013

The 2013 Atlantic hurricane season just started on June 1 but already we have our first named storm, Andrea. The system developed from a broad monsoonal gyre combined with the mid-level remnants of Hurricane Barbara from the eastern Pacific. Initially dubbed Invest 91L, the disturbance tracked slowly northward over the past few days, positioning itself north of the Yucatan Peninsula yesterday. Despite its ragged appearance on satellite imagery early in the morning, characterized by a broad low-level center with multiple mesovorticies within that and deep convection well removed from the low, a new low-level swirl developed underneath the shower and thunderstorm activity by midday, and it quickly tightened. A recon flight into the system revealed a closed center with plenty of tropical storm-force winds in the region of thunderstorms. Overnight, Andrea steadily strengthened despite forecasts of only slow intensification, and the system moved ashore the Big Bend of Florida earlier this evening, with winds of 65 mph. Current infrared images show Andrea has weakened since that time, likely a result of stronger wind shear from an approaching upper-level trough, drier air from the western Gulf of Mexico, and the fact that the storm is now inland. As of the latest advisory from the National Hurricane Center, the cyclone had sustained winds of 45 mph and a minimum barometric pressure of 993 millibars; Andrea is moving northeast at 15 mph. Tropical cyclone watches and warning remain in effect, listed below:

A Tropical Storm Warning is in effect for...
- The U.S. East Coast stretching from Flagler Beach, Florida to Cape Charles Light, Virginia
- The Pamlico and Albemarle sounds
- The lower Chesapeake Bay south of New Point Comfort

A Tropical Storm Warning indicates sustained winds of at least 39 mph are expected to occur across the warned area within 36 hours. In this case, within 24 hours.


Figure 1. Infrared imagery of Tropical Storm Andrea.

Forecast for Andrea & Impacts
Andrea is expected to continue its forward motion towards the northeast for much of the remainder of its life, ahead of the broad upper-level trough currently positioned across the Ohio River Valley. Much of the model guidance remains in agreement for a track across coastal portions of Georgia and South Carolina tonight, eastern North Carolina during the day tomorrow, out into the Atlantic southeast of Rhode Island early Saturday, over southern Newfoundland late Saturday, and ultimately out in the open north Atlantic by late Sunday. While doing so, Andrea is not expected to strengthen and should instead slowly weaken. The emphasis should be placed on slowly as the storm should become baroclinically supported tomorrow, meaning it will likely lose most of its tropical characteristics.

Regardless of strength, Tropical Storm Andrea is expected to impact the United States quite severely. Winds of tropical storm-force are likely to overspread Georgia and the Carolinas tonight and tomorrow; in conjunction with rainfall totals of 3 to 6 inches, these winds may be enough to uproot weakened trees. This may lead to sporadic power outages anywhere along the Eastern Seaboard. As far as storm surge is concerned, counter-clockwise winds onto the coastline of North Carolina and South Carolina during the day tomorrow are expected to "pile" the water onshore, leading to sea level rise of 1 to 2 feet as it occurs during high tide. Coastal regions may experience minor flooding. The main threat, at least through tomorrow, will be the threat for tornadoes. With southerly flow at 500 millibars and southwesterly flow at 850 millibars across North Carolina during the day tomorrow, wind shear may be sufficient to power low-topped supercells. Numerous EF0 and EF1s were already spawned across the state of Florida today. If a tornado warning is issued for your location you need to heed the warning. And be sure you have means to be notified of that warning...there are numerous apps for your phone, and if you have a NOAA Weather Radio, use it!

Invest 92L: the overlooked storm
As if tracking Andrea weren't enough for the first week of hurricane season, we also have a well-defined tropical disturbance in the central Atlantic. Yes, I did say central Atlantic. The National Hurricane Center has effectively dubbed this Invest 92L, though it has remained an organized entity since it left Africa on May 31. Though the system is being sheared now and its low-level circulation is exposed, 92L has had the classic appearance of a tropical cyclone over the past two days. Numerous ASCAT and OSCAT passes during this time have revealed a low-pressure area well separated from the Intertropical Convergence Zone with a closed, well-defined center and at least scattered deep convection atop the center. It has met the criteria of a tropical cyclone for two days now, yet the NHC just at 2pm EDT mentioned it in their 48-hour Tropical Weather Outlook, giving it a ~0% chance of tropical cyclone development (these chances were raised to 10% at 8pm EDT). The NHC does not like to upgrade "anomalies"...and a wave of this magnitude so early in the season is most certainly atypical...but a tropical cyclone is a tropical cyclone regardless of how rare it is. Hopefully this system is studied in-depth during post-season analysis and is reclassified.

Regardless of the past, 92L's time as a tropical cyclone has come and gone. The system is now feeling the effects of wind shear from a large upper-level trough that typically lies across the western Atlantic and central Atlantic during the early season, and the center of circulation is now well displaced from the deep convection. No further organization is expected as this system tracks west-northwest and continues in a high wind shear environment. The GFS and CMC models indicate this wave will slowly die as it tracks north of the Leeward Islands in a few days.

Development prospects in June
Now that Tropical Storm Andrea has moved ashore, it's time to start looking for what may be our second named storm of the 2013 Atlantic hurricane season, Barry. And even though we typically only see one June storm every two years, both the CMC and GFS...though through different means...say we may be dealing with two. The CMC shows a trough split in roughly 10 days off the Southeastern coastline, bringing ashore a well-defined area of low pressure near the Georgia-South Carolina border. The GFS indicates another monsoonal setup towards the end of June, tracking a weak tropical storm across the Yucatan and eventually into Texas. Though the MJO is expected to be in its downward pulse after this week, lessening the chances of tropical cyclone development as opposed to what they would be if the MJO were in its upward pulse, formation can never be ruled out; it has happened during the unfavorable mode of the MJO many times in the past.

Overall, I would put the prospects of another tropical cyclone in June at Medium, 30 to 50%.


Figure 2. The GFS' depiction of a tropical depression over the southern Gulf of Mexico in late June.

I'll have a new blog on Andrea tomorrow,

TropicalAnalystwx13

Tropical Weather Tropical Cyclones of 2013

Updated: 3:09 PM GMT on June 07, 2013

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Tropical Storm Andrea develops in the Gulf, huge rainfall producer for East Coast

By: TropicalAnalystwx13, 3:50 AM GMT on June 06, 2013

The first named storm of what promises to be an exceptionally active and dangerous year, Andrea, has developed in the Gulf of Mexico this evening. The upgrade comes after an Air Force hurricane hunter plane investigation into what was previously dubbed Invest 91L found a well-defined and closed low-level center underneath a deep burst of shower and thunderstorm activity. As of the latest advisory from the National Hurricane Center, Tropical Storm Andrea contains maximum sustained winds of 40 mph. The minimum barometric pressure was observed at 1002 millibars, and the cyclone is moving north at 6 mph. Nighttime infrared imagery suggests Andrea remains a disorganized, but slowly developing, tropical cyclone. The low-level center appears to be on the southwestern side of the recent deep convective burst, due mainly to moderate wind shear and very dry air to the cyclone's west. A recent microwave pass shows the center is much organized than one would otherwise believe, however. Environmental conditions are not expected to become much more favorable for intensification prior to landfall tomorrow night. And due to Andrea's forecast impacts to land, the National Hurricane Center and local National Weather Service offices have coordinates to issue advisories below:

A Tropical Storm Warning is in effect for...
- The west coast of Florida from Boca Grande to the mouth of the Ochlockonee

A Tropical Storm Watch is in effect for...
- The United States East Coast from Flagler Beach, Florida to Surface City, North Carolina

A Tropical Storm Warning indicates tropical storm-force winds of at least 39 mph are expected to occur across the warned area within 36 hours; a Tropical Storm Watch indicates tropical storm-force winds of at least 39 mph may occur within 36 hours.


Figure 1. Infrared satellite imagery of Tropical Storm Andrea.

Forecast for Andrea
The track forecast for Tropical Storm Andrea is straightforward. All of the global models, their ensembles, and the dynamical/statistical model suite indicate an accelerating track towards the north-northeast to northeast in advance of an upper-level trough currently positioned across the central United States. This should put the cyclone over northern Florida by late tomorrow night, on the coastline of South Carolina early Friday morning, and very near the southeastern coast of Newfoundland by late on Saturday. The system is expected to turn more easterly thereafter as it becomes embedded within the high latitude flow and begins to interact with a larger extratropical cyclone southeast of Greenland.

The intensity forecast for Andrea is seemingly straightforward as well. The cyclone remains embedded within a marginally favorable environment for intensification, marked with 20-25 knots of westerly wind shear, sea surface temperatures of 25-26 °C, and relative humidity values in the lower 60s(%). A majority of the statistical and global models foresee very little change in strength with Tropical Storm Andrea prior to landfall in Florida tomorrow night, with slow weakening thereafter. Given what the storm has to work with over the next 24 hours, my forecast is slightly above the models' prior to landfall with a peak intensity of 50 mph, with little change thereafter. Baroclinic forcing as a result of the upper-level trough is likely to help the cyclone maintain intensity as a post-tropical or extratropical entity through 120 hours.

...MAX WINDS...

INIT 06/0300Z 35 KT 40 MPH
12H 06/1200Z 40 KT 45 MPH
24H 07/0000Z 45 KT 50 MPH...MOVING ASHORE
36H 07/1200Z 40 KT 45 MPH
48H 08/0000Z 20 KT 45 MPH...POST-TROP/EXTRATROP
72H 09/0000Z 15 KT 40 MPH...POST-TROP/EXTRATROP
96H 10/0000Z 15 KT 40 MPH...POST-TROP/EXTRATROP
120H 11/0000Z 35 KT 40 MPH...POST-TROP/EXTRATROP

Forecast impacts

Via the National Hurricane Center:

STORM SURGE...THE COMBINATION OF A STORM SURGE AND THE TIDE WILL
CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE FLOODED BY RISING
WATERS. THE WATER COULD REACH THE FOLLOWING HEIGHTS ABOVE GROUND
IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH TIDE...

TAMPA BAY NORTHWARD TO APALACHICOLA...2 TO 4 FT
FLORIDA WEST COAST SOUTH OF TAMPA BAY...1 TO 2 FT

THE DEEPEST WATER WILL OCCUR ALONG THE IMMEDIATE COAST NEAR AND TO
THE SOUTH OF THE LANDFALL LOCATION. SURGE-RELATED FLOODING DEPENDS
ON THE RELATIVE TIMING OF THE SURGE AND THE TIDAL CYCLE...AND CAN
VARY GREATLY OVER SHORT DISTANCES. FOR INFORMATION SPECIFIC TO
YOUR AREA...PLEASE SEE PRODUCTS ISSUED BY YOUR LOCAL NATIONAL
WEATHER SERVICE OFFICE.

RAINFALL...ANDREA IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF
3 TO 6 INCHES OVER MUCH OF THE FLORIDA PENINSULA...EASTERN PARTS OF
THE FLORIDA PANHANDLE...AND SOUTHEASTERN GEORGIA...WITH ISOLATED
MAXIMUM AMOUNTS OF 8 INCHES POSSIBLE. TOTAL RAIN ACCUMULATIONS OF
2 TO 4 INCHES ARE ALSO EXPECTED OVER EASTERN SOUTH CAROLINA AND
EASTERN NORTH CAROLINA.

WIND...TROPICAL STORM CONDITIONS ARE EXPECTED TO FIRST REACH THE
COAST WITHIN THE WARNING AREA BY THURSDAY AFTERNOON...MAKING OUTSIDE
PREPARATIONS DIFFICULT OR DANGEROUS. TROPICAL STORM CONDITIONS ARE
POSSIBLE IN THE WATCH AREA THURSDAY NIGHT AND FRIDAY.

TORNADOES...A FEW TORNADOES ARE POSSIBLE OVER THE FLORIDA PENINSULA
TONIGHT THROUGH THURSDAY...WITH THE GREATEST POTENTIAL EXPECTED ON
THURSDAY.

I'll have a new blog on Tropical Storm Andrea tomorrow,

TropicalAnalystwx13

Tropical Cyclones of 2013 Tropical Weather

Updated: 3:54 AM GMT on June 06, 2013

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About TropicalAnalystwx13

Teenager. Weather aficionado. Soccer fan. Realist. Posts subject to sarcasm. Goal: National Hurricane Center.

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