TAOI 07-24-2010

Summary: Tropical Storm Bonnie was downgraded to a Tropical Depression at 2100UTC yesterday while over the western Florida peninsula. While TD Bonnie has since emerged into the Gulf, no re-intensification has occurred, and the National Hurricane Center has discontinued all tropical storm warnings for the Gulf coast. The upper level cold low in the Gulf of Mexico has continued to move westward and is now located just off the Texas coast. Elsewhere in the tropics, upper level diffluence south of 2 upper level lows- the Gulf of Mexico low, and a second low- located just NE of Cuba, is supporting continued convection. At 1200 UTC, the National Hurricane Center had a low probability of development associated with the Caribbean convection, but this has since been discontinued. A tropical wave, formerly PGI-18L, is located over the Leeward and Windward Islands, while PGI-19L continues to slowly progress westward. The Newfoundland low has moved eastward, bringing the front with it, while a subtropical high has remained fairly stationary. A second subtropical high has developed to the south of the front at 50W, 30N.

Forecast:
The primary features of interest within the IPEX/PREDICT/GRIP domain are the Bonnie, the convection south of Cuba and Hispaniola, convection over the Bay of Campeche, and a tropical wave over the Leeward and Windward Islands (ex-PGI-18L). PGI-19L is also of interest, though currently located outside of the domain. Likewise, the cold low east of Newfoundland and accompanying front continue to propagate westward. While the low and accompanying front are not expected to impact any systems of interest in the near future, they continue to represent a break in the large scale North Atlantic flow. While the focus remains on Bonnie today, it will shift to other features tomorrow as Bonnie moves inland.

At 1500UTC, Tropical Depression Bonnie was located at 86.7W, 28N. As has been the case throughout Bonnie’s life, it is largely under the influence of an upper level cold low, now located off the Texas coast. For the last few days, Bonnie has been located in an area of moderate shear. However, shear has increased today, in part due to the combined influences of the upper level low and an upper level ridge over the eastern US. Largely due to the high shear, no re-intensification of Bonnie has occurred. While a burst of convection occurred near the center at 0400UTC today, it was ripped apart by shear, and the center is now almost entirely devoid of any deep convection. Convection is still occurring in bands to the north west of the center of circulation. Precipitable water remains high around Bonnie’s location, however water vapor imagery shows that Bonnie is becoming separated from the moisture in the Caribbean. Weak upper level divergence and lower level convergence associated with the convection to the northwest of the center of circulation are present in CIMSS analysis, however lower level vorticity has decreased in magnitude since yesterday, and vorticity is not well stacked in the 850-500mb layer. The 12Z model guidance is in very good agreement that no further development of Bonnie will occur. Even the statistical-dynamical models which had favored development throughout the life of the storm no longer predict any intensification. Therefore, the current intensity of 30 kts is expected to persist until it makes landfall later today near the Louisiana, Mississippi border.

Elsewhere, the global models do not favor the development of any other systems within the next 48 hours. The ECMWF maintains the convection in the southern Caribbean for a day or two before dissipating it. The GFS does develop an area of high 950mb vorticity in the Bay of Campeche, however it is limited spatially, slightly smaller than Bonnie’s vorticity signature, and immediately moves inland. Pouch tracking does not favor the immediate development of PGI-19L. In fact, the ECMWF doesn’t even track it. As a result, no development of any other systems is expected within the next 48 hours.

TAOI 07-22-2010

Overview:
Two tropical waves in the Atlantic are continuing to be monitored, PGI-16L/AL98, PGI-17L/AL97/TD3.  AL98 is located in the SW Gulf of Mexico near 20N, 96W.  TD3 is located at 22N, 75W.  PGI-18L is no longer being tracked on the Montgomery website.  Operations have focused on TD3 for the past several days, and it was upgraded by the National Hurricane Center (NHC) from an invest to a tropical depression at 15 UTC today after satellite imagery began to indicate a closed circulation had developed.  Tropical Storm warnings have been issued for the Keys and southern Florida coasts.  Ft Lauderdale is currently under a tropical storm watch.  The system continues to be under the influence of a strong upper tropospheric cold low which is helping to maintain a strong shear gradient near the center of TD3.  1500 UTC CIMSS analysis shows shear greater than 20 kts within a few degrees NW of the storm center.  However, to the east of the storm and over the center, shear is only 5-10kts. Due to the shear influence, convection is limited to the eastern half of the storm.  Upper level divergence is also only marginally favorable, however some good outflow is present in the eastern half of the storm.  SSTs and atmospheric moisture content over the storm center remain conducive for development, however Ocean Heat Content is not particularly high, and dry air is present to the west of the center of circulation.  Compared to yesterday, the low level vorticity is far more concentrated, and well stacked vertically.  As long as the low level center does not move ahead of the convection, it appears that there is a good chance for development into a tropical storm in the short term.  Flight operations including all 3 NASA aircraft as well as NOAA aircraft are planned over the next 3 days for this system.

The NHC has also issued an invest on PGI-16L, now AL98, and there is a 50% probability of development within the next 48 hours.   The 06UTC Ocean Prediction Center places a 1010hPa low in AL98’s location, and widespread convection is occurring around the low.  Windshear is low in this region and SST’s are sufficiently high to support genesis.  However, the low is very near land, and should reach the coast of Mexico within the next 24 hours, limiting its chances to develop.  Elsewhere in the Atlantic, a pair of 1027 hPa subtropical highs dominate the flow resulting in largely easterly surface winds from Africa through the Gulf of Mexico.  A tropical wave which separated from TD3 is being analyzed in the Caribbean at 15N, 80W, however no convection is occurring with this system. 



Forecast:



The primary forecast concern is TD3 which is centered at 22N, 75W, moving WNW at 13 kts.  Overnight it began to show signs of development and a closed circulation formed.  However, several factors are still hindering the development of TD3.  This includes dry air to the west of the storm, land influences from Cuba, and the persistent shear to the W.  The cold low is moving faster than the depression, and has moved south and west away from the storm, effectively decreasing the shear immediately over the center of the depression, and changing the direction of the shear from SW to S.  As the cold low continues to move SW, the shear is expected to eventually turn to the SE, as indicated by the SHIPS text forecast.  While the shear is not expected to be particularly favorable for development, it also is not expected to be extremely unfavorable either.  Another consideration of the cold low is that as it moves farther ahead of the depression, the downstream ridging supporting convection near Hispaniola may set up over TD3, creating a more favorable upper level environment.

The model track forecasts for TD3 have a fairly good consensus.  Almost all of the 12Z models bring TD3 between Cuba and the Keys, with the northern most tracks bringing the center over the Keys.  Within 36 hours, the system will have emerged into the Gulf, continuing a steady NW track.  A gradual northward turn is then predicted, resulting in an eventual landfall along the Louisiana or Northern Texas coasts within 72-96 hours.  The National Hurricane Center is predicting a track near the center of the model spread with a landfall in about 84 hours at the Louisiana-Texas border.   This track seems reasonable, and there is no reason to expect any substantial deviation.

There continues to be a split in the model forecasts of intensity.  The statistical-dynamical models continue to strengthen the system into a moderate tropical storm before it makes landfall, while the dynamical models show little to no strengthening, and in fact suggest the system will gradually weaken.  Because the system is now a depression, the DSHIPS/LGEM developmental data is now applicable and more faith can be placed in those forecasts.  The NHC is taking the middle road with very slight strengthening over the next several days before landfall as a 45kt tropical storm, while SHIPS and LGEM suggest a landfall intensity closer to 55kts.  00Z Pouch tracking in the GFS and NOGAPS models show high initial OW and Zeta values, however these values quickly decay, however both level off at levels around the nominal threshold for development, suggesting that development is a possibility.  While substantial development is not anticipated, it seems likely that the system will intensify into a weak tropical storm within the next 24-48 hours.

TAOI 07-21-2010

Overview:

3 PGI systems are continuing to be tracked today.  PGI-16L, PGI-17L (AL 97), and PGI-18L.  PGI-16L is emerging into the SW Gulf of Mexico from the Yucatan Peninsula at 20N, 90W.  AL 97 is located north of the Dominican Republic/Haiti border at 20N, 67W.  PGI-18L is located around 18N, 37W.  A tropical wave, separate from AL 97  is being analyzed by the OPC at 75W, just south of 18N.  Elsewhere in the Atlantic, a 1028 hPA high continues to dominate the lower levels and flow through the Caribbean, over Florida, and into the Gulf of Mexico continues to be out of the E or SE.  Looking at upper levels, an upper level low continues to persist northwest of of AL 98, while the upper-level low in the Gulf is moving over the Texas coast. 

Discussion:

AL97 showed signs of development yesterday afternoon, and ASCAT began to show signs of a circulation, or at least a turning of the winds.   However, overnight the convection dissipated and now appears very unorganized around the center of the invest location.  There is substantial convection still occurring to the southeast of the trough, south of Hispaniola and Puerto Rico, likely driven by the outflow of the previous convection to the north.  Shear remains high to the north of AL97 due to the influence of the upper level low.  However, the low is propagating east and around the same pace as AL97, meaning that the center continues to be located away from the highest shear.  It is worth pointing out that the center is more difficult to define today, due to the lack of ASCAT data, as well as the fact that almost no convection is occurring where the center has been analyzed.  On the other hand, SSTs remain high, and moisture is also high as shown in water vapor imagery and soundings from the Dominican Republic and Puerto Rico. While several models showed AL97 developing substantially yesterday, that is not the case today.  SHIPS and LGEM (with a high bias due to this not yet being a depression) still show the strongest development, however that is only to a tropical storm.  HWRF and the GFDL also show TS development, albeit briefly, before the system is downgraded to a depression.  However, even this development may be optimistic since those models require a bogus vortex, meaning that the initial condition does not necessarily reflect the actual conditions.  Most models take AL97 on a more southerly route today through the keys, and as development continues to be non-existent, a more westerly track seems reasonable.  It is worth noting that recent satellite imagery has shown an increase in convection near the center of AL97, but development is still not likely due to the lack of circulation, land influences, and the shear to the immediate north.  While development is not immediately expected within the next 24 hours, a tropical depression could form if the cold low moves far enough ahead of the trough that shear begins to decrease over the system.  Furthermore, if the system moves into the Gulf sufficiently far enough from the upper level low, it is also possible that development could occur there.

To the southeast of AL97, and area of convection has formed, seemingly originally from outflow boundaries related to AL97 yesterday.  While this area is not under the influence of any synoptic features, convection has managed to maintain itself over the past few hours.  Downflow ridging relating to the upper level low N of AL97 may be related to the sustained convection, however the ridge seems to be centered even farther downstream.  This convection has completely separated itself from AL97, and is not likely to influence the development, or lack there of, of AL97.  If convection persists for the rest of the day and overnight, there is a slight possibility of an MCS developing, which could eventually devlop into a system of interest.  HOwever, at this point it warrants nothing more than continued monitoring. 

The other waves in the Atlantic all show little to no organization or widespread convection.  Pouch tracking does not develop or strengthen any of these waves, and while they will continue to be monitored, they appear to demonstrate no risk of development.

TAOI 07-20-2010

There are 2 primary areas of interest within the experiment domain, PGI-16L and AL-97 (PGI-17L).  PGI-16L is centered east of the Yucatan Peninsula around 20N, 85W.  AL-97 is located north of Puerto Rico,  just SW of 20N,65W.  Elsewhere in the Atlantic, a pair of 1025 and 1027 hPa ridges dominates the flow resulting in largely easterly surface winds from Africa through Gulf of Mexico.  The NHC is analyzing a tropical wave in the SW Gulf of Mexico, west of 90W, however this has no PGI assignment.  This wave is associated with an upper-level low in the central Gulf, and convection is observed in this location.  While it poses no development threat, it will bring rain and thunderstorms to the eastern Texas coast within the next 2 days.  Another upper-level low remains north of AL-97, and is contributing to high shear just north of AL-97's center.  However, the center itself is in an area of relatively low shear, only 5-10 kts.  However, there is a strong shear gradient here.  Shear is low through the Gulf of Mexico and Southern Caribbean.  Finally, PGI-18L is located near 13N,30W, however pouch tracking shows no immediate threat of development.

Over the past 24 hours, PGI-16L has remained relatively unorganized, however convection has remained fairly persistent.   Satellite imagery shows a slight hint of a mid-level circulation, but no surface circulation has been observed on ASCAT.  While NOGAPS has no pouch in the 00Z run, the GFS has PGI-16L crossing the Yucatan Peninsula within the next 12 hours before losing the pouch over the SW gulf after the 36 hour forecast.

AL-97L continues to be the primary area of interest.  The NHC has a 40% probability of development within the next 48 hours as of 12Z.  Over the past 24 hours, convection has become somewhat more concentrated towards the center of the pouch.  However, a clear low level circulation is still not evident from ASCAT, however the most recent passes have not had complete coverage over the area.  Additionally, while the center is in an environment of low shear, there is a strong shear gradient just to the north.  Depending on the exact track of AL-97, it could move into a region of shear greater than 30kts, or remain in an area of 20 or fewer knots.  A consensus of 12Z models seem to favor a relatively more northern track, which would bring AL-97 into the Bahamas within the next 48 hours, and approaching the southern (east) coast of Florida within 90 hours.  This track would keep the system in high shear for the immediate future and would suppress any development.

GFS and NOGAPS pouch tracking are somewhat conflicting.  While the GFS has the center moving north through higher shear, it actually develops AL-97 fairly quickly resulting in OW and Zeta values literally off the chart.  On the other hand, NOGAPS develops the system very little over the next 120 hours while shear remains relatively low due to a more southerly predicted path.  A consensus model intensity forecast would be the development of a tropical storm within the next 36-48 hours, however due to the lack of a defined surface circulation, and the expected track through an area of high shear, I don't expect much development within the next 48 hours unless a circulation does develop

2010-07-16 Tropical Areas of Interest

Abbreviated test discussion...

Atl basin remains dominated by high pressure. PGI-16,16N, and 17 all continue to propagate slowly westward. The Colombian low, also has progressed westward, while a trough approaches southern Florida and another is in the Gulf. The NHC has a low probability (10%) of development for the region around Columbia and Panama, as well as in the Gulf. However, convection in these locations remains unorganized. Global models all agree in developing nothing over the next 48 hours. An emerging AEW wave persists in the GFS and will be monitored over the next week or so as it approaches the GRIP domain.