Excerpt from the evening Tropical Weather Discussion from NHC/ TPC.
TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU APR 10 2008

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

ATLANTIC OCEAN E OF 40W...
OTHERWISE...AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDS FROM
W AFRICA TO JUST E OF THE LESSER ANTILLES...WITH AN AXIS RUNNING
FROM 20N06W TO 12N53W. ALTHOUGH CONVECTION HAS DECREASED OVER
THE TROPICAL ATLANTIC THE LAST FEW DAYS...THERE ARE TWO AREAS OF
INTEREST WHICH HAVE EMERGED OVER THE LAST 24 HOURS. THE FIRST
IS A CONVECTIVE CLUSTER N OF THE ITCZ...WITH WHAT APPEARS TO BE
A MID-LEVEL CYCLONIC CIRCULATION CENTERED NEAR 5N18W MOVING W AT
15 TO 20 KT. THIS FEATURE COULD BE CONSIDERED ONE OF THE
SEASONS FIRST AFRICAN EASTERLY WAVES. THE SECOND FEATURE IS
ALONG ELONGATED SURFACE TROUGH OF NORTHEASTERLIES CONVERGING
WITH EASTERLIES BETWEEN 8N AND 10N BETWEEN 45W AND 50W. EARLIER
VISIBLE SATELLITE IMAGERY REVEALED A TIGHTLY-COILED LOW- TO
PERHAPS MID-LEVEL CIRCULATION IN THE ASSOCIATED CONVECTION NEAR
9N46W....THOUGH THE CONVECTION SINCE THAT TIME HAS COLLAPSED.
http://www.srh.noaa.gov/printable.php?pil=TWD&sid=AT&date=2008-04-10%2023:46:57

Earlier rainbow enhancement of the Wave at 1800Z or 2pm EDT Thursday. Center of the circulation, at that time is near the bright red area near the bottom, center of the graphic. Directly above the "A" in APR 10 08

Taken 48 hours prior to the above picture at 2 pm EDT Tuesday.
This would appear to indicate that the current wave, in the first picture of this post, could be wave number 3.