Tropical Depression Eight

http://www.wunderground.com/tropical/tracking/at200708.html

Statement as of 5:00 PM EDT on September 12, 2007

the cloud pattern of the depression has changed very little sincethis morning with the circulation center estimated near the easternportion of the deep convection. Dvorak intensity estimatesfrom TAFB and SAB support 35 kt. Since there is some uncertaintyin the exact center location...the initial intensity will remain 30kt. The depression is currently passing about 60 nm south of NOAAbuoy 41041...which has reported a peak 1-minute wind of 28 kt and aminimum pressure of 1008.6 mb.
The initial motion estimate is 290/10. The track guidance is in goodagreement on a west-northwestward motion during the next couple ofdays. The ridge is expected to weaken as a mid-to upper-level lowdevelops several hundred miles northeast of the Leeward Islands. This is expected to cause the depression to decelerate during thenext couple of days. The new track forecast remains close to theprevious advisory through 48 hours but is adjusted a littlenorthward thereafter...in close agreement with the consensus ofhwrf...GFDL...umket...and GFS models.
Most of the intensity guidance indicates that the easterly shearcurrently affecting the cyclone should weaken during the next 24hours and the guidance suggests that depression should graduallystrengthen. The GFDL...hwrf and SHIPS models bring the depressionto hurricane strength in about 72 hours. The official forecast willremain slightly below this guidance and keep the depressionjust below hurricane strength. At days 4 and 5...strongsouthwesterly upper-level winds south of the mid-to upper-level loware expected to produce increasing shear. The GFDL responds to thisby weakening the cyclone and the official forecast will reflect someweakening late in the period.http://www.wunderground.com/tropical/at200708.disc.html#a_topad

computer models

http://www.wunderground.com/tropical/tracking/at200708_model.html#a_topad

the depression has not appreciably changed in its convective
organization or estimated intensity since this afternoon. While
Dvorak...ADT...and AMSU estimates are at minimal tropical storm
intensity...SSMI and ssmis microwave imagery suggests instead that
the center of the system is offset on the northeast side of the
convection. Upper tropospheric motion vectors show that there
remains some moderate northeasterly shear that continues to impact
the system. Since the estimated center is not well embedded within
the convection...this indicates that the system remains a tropical
depression at this time.


TD eight is south of a weak deep layered ridge which is currentlyproviding a steering of about 280/10...slightly more westward thanindicated in the previous advisory. All of the global and regionalmodels show the cyclone slowing between 24 and 48 hours in responseto the influence of an mid- to upper-level trough that is currentlynorth of 25n at the same longitude of the depression. The troughshould cutoff and retrograde west-southwestward. This has thecombined effect of weakening the west-northwestward steering aswell as inducing rather strong southwesterly shear at the longertime periods. The forecast track is the consensus of theGFS...UKMET...GFDL...and hwrf models and is slightly south of theprevious official forecast. The ECMWF and NOGAPS models arediscounted as they unrealistically take the depression northwardalmost immediately.
Though the depression is over warm 28c waters...none of theintensity guidance takes TD eight to a hurricane in the next fivedays. This may be due to the close proximity to rather dry airjust to the north and west of the system in the early time periodsand the rather sharp increase in shear at the later time periods. The intensity forecast is close to the SHIPS and lge models throughthree days and a blend of these two with the GFDL and hwrf modelsat days four and five. http://www.wunderground.com/tropical/tracking/at200708_5day.html#a_topad

TD 8 looks very organized on satellite photos that I've seen. It should definitely be watched, I think, as it has lots of water yet to cross over.

http://www.wunderground.com/tropical/tracking/at200708_model.html#a_topad

A NOAA hurricane hunter plane has been on a research mission this
evening and found 35 kt winds using the on-board stepped-frequency
microwave radiometer (sfmr). These winds match up fairly well to a
recent Quikscat pass that suggested winds of about 35 kt and
subjective Dvorak satellite estimates of 35 kt. The initial
intensity is raised to 35 kt...making this system the ninth named
storm of the year.


Moderate westerly vertical wind shear continues to affect ingrid. Most of the dynamical models keep the shear about the same for thenext 24 hours...which should allow for a modest increase instrength. Thereafter...westerly shear should intensify...likelycausing a weakening of ingrid. The official forecast keeps thesystem a tropical storm for the next few days...and could be alittle too high in the longer range as global models are showingnearly 30 kt of westerly shear in the storm's path.
The initial motion has turned a little more to the right tonight...estimated at 300/5. The track forecast is tricky as it probablyhas a strong dependence on the future intensity of ingrid. Watervapor images show a middle- to upper-level low diggingsouthwestward to the north of the system. This low has caused avery weak steering environment with only slight middle-level ridgingremaining to the northeast of the tropical cyclone. A strongertropical cyclone would probably be more responsive to thelow...and move farther to the north of the official forecast. Itis assumed that ingrid will remain weak and stay on the southernside of the guidance envelope for now.