30 August 2002

Hello Dolly! TD4 upgraded to TS Dolly, and still strengthening.

At 21Z yesterday, the NHC upgraded TD4 to a Tropical Storm, the forth
one of the season, BUT the first "purely" tropical storm... meaning that
it formed in the deep tropics, void of baroclinic influences, unlike the
previous three storms that never crossed below 25N.

The convective pattern has been very encouraging, and is the reason for
the upgrade.  The CDO is still expanding and quite cold (still around
-80C peak), and there are now obvious bands forming.  All features
appear to be symmetric about the center, meaning vertical shear is very
low.  SSTs there are approximately 28C.  At 15Z today, Dolly was located
at 10.4N 37.2W and tracking W at 14kts.  Maximum sustained winds have
reached 55kts and the central pressure has fallen to 994mb.  She is VERY
close to reaching hurricane status, probably later today.  She would be
the first hurricane of the season. (Recall that Erin was the first
hurricane of last year, on 8 Sep.)

Microwave imagery is one of the best tools to use at this stage of a
tropical cyclone's life, because the core is hidden from visible and
infrared wavelengths by the CDO.  Micowave, with a much longer
wavelength, can "see" through the clouds to reveal the inner
precipitation structure.  HOWEVER, the most recent pass of such an
instrument just barely hit the storm, not really showing enough of it to
be useful, and the last good pass was too long ago to be useful.  So, we
wait (and wish there were more microwave instruments on our growing
array of satellites).

Please visit my tropical Atlantic headquarters.

P.S. I may send out an update later today if she changes much, and then
none until Tuesday morning, as I'll be out of town for the long
weekend. Dolly will not be near any land by Tuesday; perhaps
1000km away from the closest land, which will be the Leeward Islands.

29 August 2002

Suspicious wave becomes TD4 in eastern Atlantic.

At 15Z today, the wave featured in yesterday's update was upgraded to a
Tropical Depression, the fourth of the season.  The intensity is based
on satellite imagery... persistent deep convection over or near the
low-level center.  It was located at 9.6N 32.2W and moving WNW at
14kts.  The heading and speed are expected to continue for the next few
days, perhaps turning a bit north of WNW by three days.  Winds are 30kts
with MSLP of 1007mb.  Although the environment is favorable (low shear,
warm SST, climatology), the forecast track moves it into much less
favorable conditions.  So, it may strengthen a bit in the short term,
likely becoming the fourth named storm, but may run into big problems as
the weekend comes to a close due to vertical shear.  If the forecast
track verifies, TD4 will not threaten any land mass.

Please visit my tropical Atlantic headquarters.

28 August 2002

Tropical wave near Cape Verde Islands attracts some interest.

For perhaps the first time this year, one of the many tropical waves to
exit the African coast has held its own as it traverses the open waters
of the tropical eastern Atlantic.  The wave in question is currently at
about 9N 27W and tracking W at 10kts.  Healthy signs include an obvious
low-level circulation (featuring a 1009mb Low), and convection that
continues to intensify.  The CDO has become larger and colder over the
past few hours, now with coldest tops at -80C.  Although the CDO is
slightly displaced to the SE from the low-level center, the difference
is not great, and so I suspect either the convection will shift to meet
the center or the center will shift to meet the convection.  VIS and IR
imagery both reveal organization, and although the last pass of a
high-res microwave instrument did not show much structure, the next pass
is at about 1200 MDT, and might show us a clearer picture of what's
going on under the developing CDO.

The SST there is about 28C, and that will change little (perhaps
decrease by a degree) in the next few days, before steadily increasing
once it makes it to 50W.  The vertical shear is also favorable, easterly
at 10kts now, and expected to decrease.  Lastly, it's entering the
climatologically favored time for "Cape Verde storms" to form, and there
seems to be something to be said for that.

If this system does continue to organize and become a named storm, it
would be the first purely tropical system of the year (the previous
three have been baroclinically initiated or enhanced).  The next
numbers/names on deck are TD4 then Dolly.

Models do not yet agree on a solution... one extreme is completely
dissolving the system within 5 days, while the other extreme intensifies
it and moves it WNW toward the Greater Antilles in 5 days.  Too early to
tell for sure, but the 500mb heights indicate to me that the westerly
course will persist for at least 2-3 days.
Please visit my tropical Atlantic headquarters.

09 August 2002

Bertha makes landfall, Cristobal absorbed into trough.

Bertha never made it to TS strength... the burst in convection yesterday
morning was short-lived and the highlight of her reincarnation.  Since
then, convection was minimal and the circulation center got harder and
harder to find.  She made landfall Friday morning shortly after 4am CDT
on Padre Island, Texas (within a few miles of where Bret hit on 8/22/99)
as a poorly-defined 25kt TD.  The last advisory was written on her this
morning at 15Z at which time she was located at 27.0N 98.0W

At 21Z yesterday, the last advisory was written on TS Cristobal, as he
was becoming immensely sheared and making the transition to
extratropical as his circulation merged with the trough.

The tropical wave that moved off Africa on Wednesday is still heading
west, currently located at about 16N 24W (basically OVER the Cape Verde
islands).  There is an obvious broad circulation with it as evident in
the visible satellite imagery, but what little convection there is is
located well to the south of the center.  However, the current southerly
10kt shear will soon reduce to 5kts.  The key inhibiting factor is the
SST's.  This time of year they just haven't warmed up out there, so it's
still 25.5C or so, and that won't change much in the near future. 
Although the chances for this wave developing are slim to none, the
numbers/names next on deck are TD4 or TS Dolly (but I think we'll have
to wait a bit longer to see them).

Please visit my tropical Atlantic headquarters.

08 August 2002

Bertha reforms, Cristobal getting absorbed into trough.

Not long after my update was sent out yesterday mentioning how healthy
the remnants of Bertha looked once she re-entered the Gulf, she was
upgraded to a Tropical Depression (at 21Z).  From what I gather, the
upgrade was based largely on the immediate and impressive effect the
water had on her convection and structure.  Since then, she has changed
little and is still moving slowly toward the southern Texas coast.

At 15Z today, TD Bertha was located at 27.6N 95.7W and tracking WSW at
7kts.  Intensity has held fairly steady at 25kts and 1010mb, but some
further strethening is not out of the question, in my opinion. 
Currently 110 miles east of Corpus Cristi and heading that way, I
wouldn't be surprised if a Tropical Storm Watch was issued for the
southern Texas coast (if the recent healthy trend in centralized deep
convection keeps up).  Over the last 6 hours or so, we've seen a drastic
return of a cold CDO, indicating that she may be on the verge of
intensifying already.  Since the speed and direction are not expected to
change much, we can anticipate a landfall at about 1am on Friday morning
on the northern side of Padre Island (just miles north of where Bret '99
hit as a CAT4 on 8/22 at 23Z), south of Corpus Christi.

TS Cristobal hasn't changed too much since the last advisory, and has
been behaving as forecasted.  The steering flow has been weak, and his
track reveals that... not much more than an eastward meander.  However,
as his circulation becomes more intertwined with the advancing trough,
the motion will pick up and become more northeasterly.  In fact, the
merging is already well underway; what remains of Cristobal is an area
of deep convection and an elongated circulation at the trailing end of a
cold front (with the primary Low over Nova Scotia).  

At any rate, NHC is still writing advisories on the storm.  The 15Z
position is 30.0N 73.8W and moving ENE at 5kts.  Winds are 40kts with
MSLP of 1000mb.  No strengthening is forecast, although it's possible
that once he's transitioned to an extratropical cyclone, the Low could
be baroclinically enhanced and winds could get stronger.  He will not
threaten land.

Lastly, there's a broad area of disturbed weather that moved off Africa
yesterday and is now at about 8N 19W.  It's got a diffuse region of
vorticity to work with, has good upper-level divergence, and but is
embedded in about 20kts of easterly vertical shear.  It is (temporarily)
moving into lower shear, so is worth watching.

Please visit my tropical Atlantic headquarters.

07 August 2002



I so appreciate getting your TC evaluations.  I hang on your every
word.  I greatly trust your evaluations.  I hope you are able to keep
this up.

Warmest regards,
Bill Gray
Please visit my tropical Atlantic headquarters.

Bertha still worth keeping an eye on, Cristobal forms from TD3.

Although advisories ceased on Bertha as of Monday morning, she has
drifted back over warm Gulf waters and is still moving very slowly. 
This COULD give her the opportunity to redevelop.  At 1630Z, I placed
the low-level center at 29.3N 93.0W based on visible imagery... moving
WSW at not much more than a drift.  Although the bulk of convection
associated with the remnants of Bertha is well to the south and
southwest of the center, new blowups are occuring very close to the
center, and if maintained, could lead to redevelopment.  If the future
track of ex-Bertha should become important, it seems to me that she'd
continue moving slowly SSW or SW toward Texas.

At 2330Z Tuesday, TD3 was upgraded to TS Cristobal based on an aircraft
recon flight into the storm.  The lastest advisory (15Z) places
Cristobal at 29.3N 76.0W and nearly stationary.  Winds are 40kts and
MSLP is 999mb.  The official NHC forecast is for a trough to pick him up
and move him rapidly ENE then NE, while turning him extratropical. 
However, there are models that allow him remain tropical and intensify
(even to a major hurricane).  Although unlikely, it's worth watching
for.  Unless the trough passes him by and easterly trades take control
again, he will not impact the US mainland.

Elsewhere in the basin, pressures are high, shear is high, and
convection is hard to come by.  For those who are interested, CSU's
Seasonal Forecast Team (led by Bill Gray) just today reduced the
expectations for the season to 9 Named Storms, 4 Hurricanes, and 1 Major
Hurricane.  Recall that as of now, we're at 3/0/0.

Please visit my tropical Atlantic headquarters.

06 August 2002

Bertha drops 5"+ over parts of MS and LA. TD3 forms off the South Carolina coast and is slowly intensifying.

Just hours after sending out my update yesterday, the invest area was
classified as Tropical Depression 3, as an aircraft flying through it
found a closed surface circulation.  Since then, little has changed:
there is still northerly shear and it's still a TD.  However, the
exposed circulation center is tight, and the convection to the south of
the center is still fairly intense, perhaps foreshadowing some
strengthening.  The northerly shear has increased to nearly 20kts,
drastically inhibiting centralized deep convection.

As of the 15Z advisory, TD3 was located at 30.3N 76.2W and drifting ESE
at 4 kts.  Winds are 30 kts with a MSLP of 1006mb.  Visible satellite
imagery shows the center at 30.4N 76.4W at 16Z, showing the meandering
nature of the storm at this point.  Micowave imagery from AMSU at 07Z
today shows a SLIGHT warm core aloft (1 deg at 250mb).  Further
intensification is expected as a mid-latitude trough approaches it and
baroclinically enhances the storm, prior to shearing it apart and
absorbing it.  If named (i.e., if sustained winds reach 35kts), it will
be Cristobal.  

Please visit my tropical Atlantic headquarters.

05 August 2002

Second Tropical Storm forms just off the Gulf coast during the weekend, #3 might be in the making soon...

At 21Z on Sunday, TD2 formed just 85 miles south of the MS coast, and
proceded to move inland while strengthening.  By 2330Z, TD2 had reached
Tropical Storm strength and became TS Bertha, who continued to head
northwest toward the LA/MS border.  Monday at 12Z, Bertha finally made
landfall near New Orleans, LA, while still meandering very slowly and
losing organization and intensity.  The latest advisory (15Z) places
Bertha at 30.8N 90.2W and tracking NNW at 10kts.  The pressure has risen
to 1010mb and the sustained winds have fallen to 25kts, downgrading her
to a Tropical Depression again.  The primary threat from this point on
is inland flooding in MS, LA, and TX.

There is a Low becoming better organized off the South Carolina coast
today. A cold CDO over the center earlier this morning aided in the
organization, now leading to the formation of outer rainbands.  It is
drifting roughly eastward and is expected to intensify further. 
Aircraft recon is planned to investigate the system closer.  This could
become TD3, or if strong enough, TS Cristobal in the near future.

Please visit my tropical Atlantic headquarters.